Class | Sequel::Dataset
In: | lib/sequel/adapters/do.rb lib/sequel/adapters/jdbc.rb lib/sequel/adapters/mysql.rb lib/sequel/adapters/postgres.rb lib/sequel/adapters/sqlite.rb lib/sequel/adapters/utils/stored_procedures.rb lib/sequel/adapters/swift.rb lib/sequel/dataset.rb lib/sequel/dataset/actions.rb lib/sequel/dataset/features.rb lib/sequel/dataset/graph.rb lib/sequel/dataset/misc.rb lib/sequel/dataset/prepared_statements.rb lib/sequel/dataset/query.rb lib/sequel/dataset/sql.rb lib/sequel/dataset/mutation.rb lib/sequel/extensions/pagination.rb lib/sequel/extensions/pretty_table.rb lib/sequel/extensions/query.rb lib/sequel/extensions/to_dot.rb
Parent: | Sequel::Dataset

A dataset represents an SQL query, or more generally, an abstract set of rows in the database. Datasets can be used to create, retrieve, update and delete records.

Query results are always retrieved on demand, so a dataset can be kept around and reused indefinitely (datasets never cache results):

      my_posts = DB[:posts].filter(:author => 'david') # no records are retrieved
      my_posts.all # records are retrieved
      my_posts.all # records are retrieved again

Most dataset methods return modified copies of the dataset (functional style), so you can reuse different datasets to access data:

      posts = DB[:posts]
      davids_posts = posts.filter(:author => 'david')
      old_posts = posts.filter('stamp < ?', Date.today - 7)
      davids_old_posts = davids_posts.filter('stamp < ?', Date.today - 7)

Datasets are Enumerable objects, so they can be manipulated using any of the Enumerable methods, such as map, inject, etc.

For more information, see the "Dataset Basics" guide.

### Contents

- Methods that execute code on the database
- Methods that describe what the dataset supports
- Methods related to dataset graphing
- Miscellaneous methods
- Methods related to prepared statements or bound variables
- Methods that return modified datasets
- User Methods relating to SQL Creation
- Internal Methods relating to SQL Creation
- Mutation methods

### Methods

<< == [] []= _insert_sql _update_sql add_graph_aliases aliased_expression_sql all and array_sql as avg bind boolean_constant_sql call call call call case_expression_sql cast_sql clause_methods clone column_all_sql columns columns! complex_expression_sql compound_from_self constant_sql count def_mutation_method def_mutation_method delete delete delete_sql distinct each each_page each_server empty? eql? except exclude exists fetch_rows fetch_rows fetch_rows fetch_rows fetch_rows fetch_rows fetch_rows filter first first_source first_source_alias first_source_table for_update from from_self function_sql get graph graph grep group group_and_count group_by hash having import insert insert insert_multiple insert_sql inspect intersect interval invert join join_clause_sql join_on_clause_sql join_table join_using_clause_sql last limit literal lock_style map max min multi_insert multi_insert_sql naked negative_boolean_constant_sql new new options_overlap or order order_append order_by order_more order_prepend ordered_expression_sql paginate placeholder_literal_string_sql prepare prepare prepare prepare prepare prepared_arg_placeholder print provides_accurate_rows_matched? qualified_identifier_sql qualify qualify_to qualify_to_first_source query quote_identifier quote_identifiers? quote_schema_table quoted_identifier range replace requires_sql_standard_datetimes? reverse reverse_order schema_and_table select select_all select_append select_hash select_map select_more select_order_map select_sql server set set_defaults set_graph_aliases set_overrides simple_select_all? single_record single_value split_alias split_multiple_result_sets sql subscript_sql sum supports_cte? supports_distinct_on? supports_intersect_except? supports_intersect_except_all? supports_is_true? supports_join_using? supports_modifying_joins? supports_multiple_column_in? supports_timestamp_timezones? supports_timestamp_usecs? supports_window_functions? to_csv to_dot to_hash to_prepared_statement truncate truncate_sql unfiltered ungraphed ungrouped union unlimited unordered unused_table_alias update update update_sql use_cursor where window_function_sql window_sql with with_recursive with_sql

### Included Modules

StoredProcedures Sequel::MySQL::DatasetMethods StoredProcedures Sequel::Postgres::DatasetMethods ::Sequel::SQLite::DatasetMethods Metaprogramming Enumerable

### Classes and Modules

Module Sequel::Dataset::ArgumentMapper
Module Sequel::Dataset::BindArgumentMethods
Module Sequel::Dataset::CallableStatementMethods
Module Sequel::Dataset::PreparedStatementMethods
Module Sequel::Dataset::StoredProcedureMethods
Module Sequel::Dataset::StoredProcedures

### Constants

PREPARED_ARG_PLACEHOLDER | = | LiteralString.new('$').freeze
PREPARED_ARG_PLACEHOLDER | = | ':'.freeze

### Attributes

convert_types | [RW] | Whether to convert some Java types to ruby types when retrieving rows. Uses the database‘s setting by default, can be set to false to roughly double performance when fetching rows.

### Public Class methods

new(db, opts={})

Use the convert_types default setting from the database

[Source]

         # File lib/sequel/adapters/jdbc.rb, line 534
    534:       def initialize(db, opts={})
    535:         @convert_types = db.convert_types
    536:         super
    537:       end

### Public Instance methods

call(type, bind_vars={}, *values, &block)

Execute the given type of statement with the hash of values.

[Source]

         # File lib/sequel/adapters/postgres.rb, line 425
    425:         def call(type, bind_vars={}, *values, &block)
    426:           ps = to_prepared_statement(type, values)
    427:           ps.extend(BindArgumentMethods)
    428:           ps.call(bind_vars, &block)
    429:         end

call(type, bind_arguments={}, *values, &block)

MySQL is different in that it supports prepared statements but not bound variables outside of prepared statements. The default implementation breaks the use of subselects in prepared statements, so extend the temporary prepared statement that this creates with a module that fixes it.

[Source]

         # File lib/sequel/adapters/mysql.rb, line 351
    351:       def call(type, bind_arguments={}, *values, &block)
    352:         ps = to_prepared_statement(type, values)
    353:         ps.extend(CallableStatementMethods)
    354:         ps.call(bind_arguments, &block)
    355:       end

call(type, bind_vars={}, *values, &block)

Execute the given type of statement with the hash of values.

[Source]

         # File lib/sequel/adapters/sqlite.rb, line 280
    280:       def call(type, bind_vars={}, *values, &block)
    281:         ps = to_prepared_statement(type, values)
    282:         ps.extend(BindArgumentMethods)
    283:         ps.call(bind_vars, &block)
    284:       end

delete()

Delete rows matching this dataset

[Source]

         # File lib/sequel/adapters/mysql.rb, line 358
    358:       def delete
    359:         execute_dui(delete_sql){|c| return c.affected_rows}
    360:       end

fetch_rows(sql) {|s| ...}

Yield all rows matching this dataset. If the dataset is set to split multiple statements, yield arrays of hashes one per statement instead of yielding results for all statements as hashes.

[Source]

         # File lib/sequel/adapters/mysql.rb, line 365
    365:       def fetch_rows(sql, &block)
    366:         execute(sql) do |r|
    367:           i = -1
    368:           cols = r.fetch_fields.map do |f|
    369:             # Pretend tinyint is another integer type if its length is not 1, to
    370:             # avoid casting to boolean if Sequel::MySQL.convert_tinyint_to_bool
    371:             # is set.
    372:             type_proc = f.type == 1 && f.length != 1 ? MYSQL_TYPES[2] : MYSQL_TYPES[f.type]
    373:             [output_identifier(f.name), type_proc, i+=1]
    374:           end
    375:           @columns = cols.map{|c| c.first}
    376:           if opts[:split_multiple_result_sets]
    377:             s = []
    378:             yield_rows(r, cols){|h| s << h}
    379:             yield s
    380:           else
    381:             yield_rows(r, cols, &block)
    382:           end
    383:         end
    384:         self
    385:       end

fetch_rows(sql, &block)

Set the columns and yield the hashes to the block.

[Source]

         # File lib/sequel/adapters/swift.rb, line 139
    139:       def fetch_rows(sql, &block)
    140:         execute(sql) do |res|
    141:           @columns = res.fields
    142:           res.each(&block)
    143:         end
    144:         self
    145:       end

fetch_rows(sql, &block)

Correctly return rows from the database and return them as hashes.

[Source]

         # File lib/sequel/adapters/jdbc.rb, line 540
    540:       def fetch_rows(sql, &block)
    541:         execute(sql){|result| process_result_set(result, &block)}
    542:         self
    543:       end

fetch_rows(sql) {|row| ...}

Yield a hash for each row in the dataset.

[Source]

         # File lib/sequel/adapters/sqlite.rb, line 287
    287:       def fetch_rows(sql)
    288:         execute(sql) do |result|
    289:           i = -1
    290:           type_procs = result.types.map{|t| SQLITE_TYPES[base_type_name(t)]}
    291:           cols = result.columns.map{|c| i+=1; [output_identifier(c), i, type_procs[i]]}
    292:           @columns = cols.map{|c| c.first}
    293:           result.each do |values|
    294:             row = {}
    295:             cols.each do |name,i,type_proc|
    296:               v = values[i]
    297:               if type_proc && v.is_a?(String)
    298:                 v = type_proc.call(v)
    299:               end
    300:               row[name] = v
    301:             end
    302:             yield row
    303:           end
    304:         end
    305:       end

fetch_rows(sql, &block)

Yield all rows returned by executing the given SQL and converting the types.

[Source]

         # File lib/sequel/adapters/postgres.rb, line 317
    317:       def fetch_rows(sql, &block)
    318:         return cursor_fetch_rows(sql, &block) if @opts[:cursor]
    319:         execute(sql){|res| yield_hash_rows(res, fetch_rows_set_cols(res), &block)}
    320:       end

fetch_rows(sql) {|h| ...}

Execute the SQL on the database and yield the rows as hashes with symbol keys.

[Source]

         # File lib/sequel/adapters/do.rb, line 175
    175:       def fetch_rows(sql)
    176:         execute(sql) do |reader|
    177:           cols = @columns = reader.fields.map{|f| output_identifier(f)}
    178:           while(reader.next!) do
    179:             h = {}
    180:             cols.zip(reader.values).each{|k, v| h[k] = v}
    181:             yield h
    182:           end
    183:         end
    184:         self
    185:       end

graph(*)

Don‘t allow graphing a dataset that splits multiple statements

[Source]

         # File lib/sequel/adapters/mysql.rb, line 388
    388:       def graph(*)
    389:         raise(Error, "Can't graph a dataset that splits multiple result sets") if opts[:split_multiple_result_sets]
    390:         super
    391:       end

insert(*values)

Insert a new value into this dataset

[Source]

         # File lib/sequel/adapters/mysql.rb, line 394
    394:       def insert(*values)
    395:         execute_dui(insert_sql(*values)){|c| return c.insert_id}
    396:       end

prepare(type, name=nil, *values)

Prepare the given type of query with the given name and store it in the database. Note that a new native prepared statement is created on each call to this prepared statement.

[Source]

         # File lib/sequel/adapters/sqlite.rb, line 310
    310:       def prepare(type, name=nil, *values)
    311:         ps = to_prepared_statement(type, values)
    312:         ps.extend(PreparedStatementMethods)
    313:         if name
    314:           ps.prepared_statement_name = name
    315:           db.prepared_statements[name] = ps
    316:         end
    317:         ps.prepared_sql
    318:         ps
    319:       end

prepare(type, name=nil, *values)

Store the given type of prepared statement in the associated database with the given name.

[Source]

         # File lib/sequel/adapters/mysql.rb, line 400
    400:       def prepare(type, name=nil, *values)
    401:         ps = to_prepared_statement(type, values)
    402:         ps.extend(PreparedStatementMethods)
    403:         if name
    404:           ps.prepared_statement_name = name
    405:           db.prepared_statements[name] = ps
    406:         end
    407:         ps
    408:       end

prepare(type, name=nil, *values)

Prepare the given type of statement with the given name, and store it in the database to be called later.

[Source]

         # File lib/sequel/adapters/postgres.rb, line 433
    433:         def prepare(type, name=nil, *values)
    434:           ps = to_prepared_statement(type, values)
    435:           ps.extend(PreparedStatementMethods)
    436:           if name
    437:             ps.prepared_statement_name = name
    438:             db.prepared_statements[name] = ps
    439:           end
    440:           ps
    441:         end

prepare(type, name=nil, *values)

Create a named prepared statement that is stored in the database (and connection) for reuse.

[Source]

         # File lib/sequel/adapters/jdbc.rb, line 547
    547:       def prepare(type, name=nil, *values)
    548:         ps = to_prepared_statement(type, values)
    549:         ps.extend(PreparedStatementMethods)
    550:         if name
    551:           ps.prepared_statement_name = name
    552:           db.prepared_statements[name] = ps
    553:         end
    554:         ps
    555:       end

prepared_arg_placeholder()

PostgreSQL uses $N for placeholders instead of ?, so use a $ as the placeholder.

[Source]

         # File lib/sequel/adapters/postgres.rb, line 447
    447:         def prepared_arg_placeholder
    448:           PREPARED_ARG_PLACEHOLDER
    449:         end

replace(*args)

Replace (update or insert) the matching row.

[Source]

         # File lib/sequel/adapters/mysql.rb, line 411
    411:       def replace(*args)
    412:         execute_dui(replace_sql(*args)){|c| return c.insert_id}
    413:       end

split_multiple_result_sets()

Makes each yield arrays of rows, with each array containing the rows for a given result set. Does not work with graphing. So you can submit SQL with multiple statements and easily determine which statement returned which results.

Modifies the row_proc of the returned dataset so that it still works as expected (running on the hashes instead of on the arrays of hashes). If you modify the row_proc afterward, note that it will receive an array of hashes instead of a hash.

[Source]

         # File lib/sequel/adapters/mysql.rb, line 424
    424:       def split_multiple_result_sets
    425:         raise(Error, "Can't split multiple statements on a graphed dataset") if opts[:graph]
    426:         ds = clone(:split_multiple_result_sets=>true)
    427:         ds.row_proc = proc{|x| x.map{|h| row_proc.call(h)}} if row_proc
    428:         ds
    429:       end

update(values={})

Update the matching rows.

[Source]

         # File lib/sequel/adapters/mysql.rb, line 432
    432:       def update(values={})
    433:         execute_dui(update_sql(values)){|c| return c.affected_rows}
    434:       end

use_cursor(opts={})

Uses a cursor for fetching records, instead of fetching the entire result set at once. Can be used to process large datasets without holding all rows in memory (which is what the underlying drivers do by default). Options:

- :rows_per_fetch - the number of rows per fetch (default 1000). Higher numbers result in fewer queries but greater memory use.

Usage:

      DB[:huge_table].use_cursor.each{|row| p row}
      DB[:huge_table].use_cursor(:rows_per_fetch=>10000).each{|row| p row}

This is untested with the prepared statement/bound variable support, and unlikely to work with either.

[Source]

         # File lib/sequel/adapters/postgres.rb, line 337
    337:       def use_cursor(opts={})
    338:         clone(:cursor=>{:rows_per_fetch=>1000}.merge(opts))
    339:       end

## Methods that execute code on the database

These methods all execute the dataset‘s SQL on the database. They don‘t return modified datasets, so if used in a method chain they should be the last method called.

### Constants

ACTION_METHODS | = | %w'<< [] []= all avg count columns columns! delete each empty? fetch_rows first get import insert insert_multiple interval last map max min multi_insert range select_hash select_map select_order_map set single_record single_value sum to_csv to_hash truncate update'.map{|x| x.to_sym} |  | Action methods defined by Sequel that execute code on the database.

### Public Instance methods

<<(*args)

Alias for insert, but not aliased directly so subclasses don‘t have to override both methods.

[Source]

        # File lib/sequel/dataset/actions.rb, line 18
    18:     def <<(*args)
    19:       insert(*args)
    20:     end

[](*conditions)

Returns the first record matching the conditions. Examples:

      DB[:table][:id=>1] # SELECT * FROM table WHERE (id = 1) LIMIT 1
      # => {:id=1}

[Source]

        # File lib/sequel/dataset/actions.rb, line 26
    26:     def [](*conditions)
    27:       raise(Error, ARRAY_ACCESS_ERROR_MSG) if (conditions.length == 1 and conditions.first.is_a?(Integer)) or conditions.length == 0
    28:       first(*conditions)
    29:     end

[]=(conditions, values)

Update all records matching the conditions with the values specified. Returns the number of rows affected.

      DB[:table][:id=>1] = {:id=>2} # UPDATE table SET id = 2 WHERE id = 1
      # => 1 # number of rows affected

[Source]

        # File lib/sequel/dataset/actions.rb, line 36
    36:     def []=(conditions, values)
    37:       filter(conditions).update(values)
    38:     end

all(&block)

Returns an array with all records in the dataset. If a block is given, the array is iterated over after all items have been loaded.

      DB[:table].all # SELECT * FROM table
      # => [{:id=>1, ...}, {:id=>2, ...}, ...]

      # Iterate over all rows in the table
      DB[:table].all{|row| p row}

[Source]

        # File lib/sequel/dataset/actions.rb, line 48
    48:     def all(&block)
    49:       a = []
    50:       each{|r| a << r}
    51:       post_load(a)
    52:       a.each(&block) if block
    53:       a
    54:     end

avg(column)

Returns the average value for the given column.

      DB[:table].avg(:number) # SELECT avg(number) FROM table LIMIT 1
      # => 3

[Source]

        # File lib/sequel/dataset/actions.rb, line 60
    60:     def avg(column)
    61:       aggregate_dataset.get{avg(column)}
    62:     end

columns()

Returns the columns in the result set in order as an array of symbols. If the columns are currently cached, returns the cached value. Otherwise, a SELECT query is performed to retrieve a single row in order to get the columns.

If you are looking for all columns for a single table and maybe some information about each column (e.g. database type), see `Database#schema`.

      DB[:table].columns
      # => [:id, :name]

[Source]

        # File lib/sequel/dataset/actions.rb, line 73
    73:     def columns
    74:       return @columns if @columns
    75:       ds = unfiltered.unordered.clone(:distinct => nil, :limit => 1)
    76:       ds.each{break}
    77:       @columns = ds.instance_variable_get(:@columns)
    78:       @columns || []
    79:     end

columns!()

Ignore any cached column information and perform a query to retrieve a row in order to get the columns.

      DB[:table].columns!
      # => [:id, :name]

[Source]

        # File lib/sequel/dataset/actions.rb, line 86
    86:     def columns!
    87:       @columns = nil
    88:       columns
    89:     end

count()

Returns the number of records in the dataset.

      DB[:table].count # SELECT COUNT(*) AS count FROM table LIMIT 1
      # => 3

[Source]

        # File lib/sequel/dataset/actions.rb, line 95
    95:     def count
    96:       aggregate_dataset.get{COUNT(:*){}.as(count)}.to_i
    97:     end

delete()

Deletes the records in the dataset. The returned value should be number of records deleted, but that is adapter dependent.

      DB[:table].delete # DELETE * FROM table
      # => 3

[Source]

         # File lib/sequel/dataset/actions.rb, line 104
    104:     def delete
    105:       execute_dui(delete_sql)
    106:     end

each() {|row_proc.call(r)}| ...}

Iterates over the records in the dataset as they are yielded from the database adapter, and returns self.

      DB[:table].each{|row| p row} # SELECT * FROM table

Note that this method is not safe to use on many adapters if you are running additional queries inside the provided block. If you are running queries inside the block, you should use `all` instead of `each` for the outer queries, or use a separate thread or shard inside `each`:

[Source]

         # File lib/sequel/dataset/actions.rb, line 117
    117:     def each(&block)
    118:       if @opts[:graph]
    119:         graph_each(&block)
    120:       elsif row_proc = @row_proc
    121:         fetch_rows(select_sql){|r| yield row_proc.call(r)}
    122:       else
    123:         fetch_rows(select_sql, &block)
    124:       end
    125:       self
    126:     end

empty?()

Returns true if no records exist in the dataset, false otherwise

      DB[:table].empty? # SELECT 1 FROM table LIMIT 1
      # => false

[Source]

         # File lib/sequel/dataset/actions.rb, line 132
    132:     def empty?
    133:       get(1).nil?
    134:     end

fetch_rows(sql)

Executes a select query and fetches records, yielding each record to the supplied block. The yielded records should be hashes with symbol keys. This method should probably should not be called by user code, use `each` instead.

[Source]

         # File lib/sequel/dataset/actions.rb, line 140
    140:     def fetch_rows(sql)
    141:       raise NotImplemented, NOTIMPL_MSG
    142:     end

first(*args, &block)

If a integer argument is given, it is interpreted as a limit, and then returns all matching records up to that limit. If no argument is passed, it returns the first matching record. If any other type of argument(s) is passed, it is given to filter and the first matching record is returned. If a block is given, it is used to filter the dataset before returning anything. Examples:

      DB[:table].first # SELECT * FROM table LIMIT 1
      # => {:id=>7}

      DB[:table].first(2) # SELECT * FROM table LIMIT 2
      # => [{:id=>6}, {:id=>4}]

      DB[:table].first(:id=>2) # SELECT * FROM table WHERE (id = 2) LIMIT 1
      # => {:id=>2}

      DB[:table].first("id = 3") # SELECT * FROM table WHERE (id = 3) LIMIT 1
      # => {:id=>3}

      DB[:table].first("id = ?", 4) # SELECT * FROM table WHERE (id = 4) LIMIT 1
      # => {:id=>4}

      DB[:table].first{id > 2} # SELECT * FROM table WHERE (id > 2) LIMIT 1
      # => {:id=>5}

      DB[:table].first("id > ?", 4){id < 6} # SELECT * FROM table WHERE ((id > 4) AND (id < 6)) LIMIT 1
      # => {:id=>5}

      DB[:table].first(2){id < 2} # SELECT * FROM table WHERE (id < 2) LIMIT 2
      # => [{:id=>1}]

[Source]

         # File lib/sequel/dataset/actions.rb, line 174
    174:     def first(*args, &block)
    175:       ds = block ? filter(&block) : self
    176:
    177:       if args.empty?
    178:         ds.single_record
    179:       else
    180:         args = (args.size == 1) ? args.first : args
    181:         if Integer === args
    182:           ds.limit(args).all
    183:         else
    184:           ds.filter(args).single_record
    185:         end
    186:       end
    187:     end

get(column=nil, &block)

Return the column value for the first matching record in the dataset. Raises an error if both an argument and block is given.

      DB[:table].get(:id) # SELECT id FROM table LIMIT 1
      # => 3

      ds.get{sum(id)} # SELECT sum(id) FROM table LIMIT 1
      # => 6

[Source]

         # File lib/sequel/dataset/actions.rb, line 197
    197:     def get(column=nil, &block)
    198:       if column
    199:         raise(Error, ARG_BLOCK_ERROR_MSG) if block
    200:         select(column).single_value
    201:       else
    202:         select(&block).single_value
    203:       end
    204:     end

import(columns, values, opts={})

Inserts multiple records into the associated table. This method can be used to efficiently insert a large number of records into a table in a single query if the database supports it. Inserts are automatically wrapped in a transaction.

This method is called with a columns array and an array of value arrays:

      DB[:table].import([:x, :y], [[1, 2], [3, 4]])
      # INSERT INTO table (x, y) VALUES (1, 2)
      # INSERT INTO table (x, y) VALUES (3, 4)

This method also accepts a dataset instead of an array of value arrays:

      DB[:table].import([:x, :y], DB[:table2].select(:a, :b))
      # INSERT INTO table (x, y) SELECT a, b FROM table2

The method also accepts a :slice or :commit_every option that specifies the number of records to insert per transaction. This is useful especially when inserting a large number of records, e.g.:

      # this will commit every 50 records
      dataset.import([:x, :y], [[1, 2], [3, 4], ...], :slice => 50)

[Source]

         # File lib/sequel/dataset/actions.rb, line 228
    228:     def import(columns, values, opts={})
    229:       return @db.transaction{insert(columns, values)} if values.is_a?(Dataset)
    230:
    231:       return if values.empty?
    232:       raise(Error, IMPORT_ERROR_MSG) if columns.empty?
    233:
    234:       if slice_size = opts[:commit_every] || opts[:slice]
    235:         offset = 0
    236:         loop do
    237:           @db.transaction(opts){multi_insert_sql(columns, values[offset, slice_size]).each{|st| execute_dui(st)}}
    238:           offset += slice_size
    239:           break if offset >= values.length
    240:         end
    241:       else
    242:         statements = multi_insert_sql(columns, values)
    243:         @db.transaction{statements.each{|st| execute_dui(st)}}
    244:       end
    245:     end

insert(*values)

Inserts values into the associated table. The returned value is generally the value of the primary key for the inserted row, but that is adapter dependent.

`insert` handles a number of different argument formats:

- No arguments, single empty hash - Uses DEFAULT VALUES
- Single hash - Most common format, treats keys as columns an values as values
- Single array - Treats entries as values, with no columns
- Two arrays - Treats first array as columns, second array as values
- Single Dataset - Treats as an insert based on a selection from the dataset given, with no columns
- Array and dataset - Treats as an insert based on a selection from the dataset given, with the columns given by the array.

  DB[:items].insert # INSERT INTO items DEFAULT VALUES

  DB[:items].insert({}) # INSERT INTO items DEFAULT VALUES

  DB[:items].insert() # INSERT INTO items VALUES (1, 2, 3)

  DB[:items].insert([:a, :b], [1,2]) # INSERT INTO items (a, b) VALUES (1, 2)

  DB[:items].insert(:a => 1, :b => 2) # INSERT INTO items (a, b) VALUES (1, 2)

  DB[:items].insert(DB) # INSERT INTO items SELECT * FROM old_items

  DB[:items].insert([:a, :b], DB[:old_items]) # INSERT INTO items (a, b) SELECT * FROM old_items

[Source]

         # File lib/sequel/dataset/actions.rb, line 280
    280:     def insert(*values)
    281:       execute_insert(insert_sql(*values))
    282:     end

insert_multiple(array, &block)

Inserts multiple values. If a block is given it is invoked for each item in the given array before inserting it. See `multi_insert` as a possible faster version that inserts multiple records in one SQL statement.

      DB[:table].insert_multiple([{:x=>1}, {:x=>2}])
      # INSERT INTO table (x) VALUES (1)
      # INSERT INTO table (x) VALUES (2)

      DB[:table].insert_multiple([{:x=>1}, {:x=>2}]){|row| row[:y] = row[:x] * 2}
      # INSERT INTO table (x, y) VALUES (1, 2)
      # INSERT INTO table (x, y) VALUES (2, 4)

[Source]

         # File lib/sequel/dataset/actions.rb, line 296
    296:     def insert_multiple(array, &block)
    297:       if block
    298:         array.each {|i| insert(block[i])}
    299:       else
    300:         array.each {|i| insert(i)}
    301:       end
    302:     end

interval(column)

Returns the interval between minimum and maximum values for the given column.

      DB[:table].interval(:id) # SELECT (max(id) - min(id)) FROM table LIMIT 1
      # => 6

[Source]

         # File lib/sequel/dataset/actions.rb, line 309
    309:     def interval(column)
    310:       aggregate_dataset.get{max(column) - min(column)}
    311:     end

last(*args, &block)

Reverses the order and then runs first. Note that this will not necessarily give you the last record in the dataset, unless you have an unambiguous order. If there is not currently an order for this dataset, raises an `Error`.

      DB[:table].order(:id).last # SELECT * FROM table ORDER BY id DESC LIMIT 1
      # => {:id=>10}

      DB[:table].order(:id.desc).last(2) # SELECT * FROM table ORDER BY id ASC LIMIT 2
      # => [{:id=>1}, {:id=>2}]

[Source]

         # File lib/sequel/dataset/actions.rb, line 323
    323:     def last(*args, &block)
    324:       raise(Error, 'No order specified') unless @opts[:order]
    325:       reverse.first(*args, &block)
    326:     end

map(column=nil, &block)

Maps column values for each record in the dataset (if a column name is given), or performs the stock mapping functionality of `Enumerable` otherwise. Raises an `Error` if both an argument and block are given.

      DB[:table].map(:id) # SELECT * FROM table
      # => [1, 2, 3, ...]

      DB[:table].map{|r| r[:id] * 2} # SELECT * FROM table
      # => [2, 4, 6, ...]

[Source]

         # File lib/sequel/dataset/actions.rb, line 337
    337:     def map(column=nil, &block)
    338:       if column
    339:         raise(Error, ARG_BLOCK_ERROR_MSG) if block
    340:         super(){|r| r[column]}
    341:       else
    342:         super(&block)
    343:       end
    344:     end

max(column)

Returns the maximum value for the given column.

      DB[:table].max(:id) # SELECT max(id) FROM table LIMIT 1
      # => 10

[Source]

         # File lib/sequel/dataset/actions.rb, line 350
    350:     def max(column)
    351:       aggregate_dataset.get{max(column)}
    352:     end

min(column)

Returns the minimum value for the given column.

      DB[:table].min(:id) # SELECT min(id) FROM table LIMIT 1
      # => 1

[Source]

         # File lib/sequel/dataset/actions.rb, line 358
    358:     def min(column)
    359:       aggregate_dataset.get{min(column)}
    360:     end

multi_insert(hashes, opts={})

This is a front end for import that allows you to submit an array of hashes instead of arrays of columns and values:

      DB[:table].multi_insert([{:x => 1}, {:x => 2}])
      # INSERT INTO table (x) VALUES (1)
      # INSERT INTO table (x) VALUES (2)

Be aware that all hashes should have the same keys if you use this calling method, otherwise some columns could be missed or set to null instead of to default values.

You can also use the :slice or :commit_every option that import accepts.

[Source]

         # File lib/sequel/dataset/actions.rb, line 374
    374:     def multi_insert(hashes, opts={})
    375:       return if hashes.empty?
    376:       columns = hashes.first.keys
    377:       import(columns, hashes.map{|h| columns.map{|c| h[c]}}, opts)
    378:     end

range(column)

Returns a `Range` instance made from the minimum and maximum values for the given column.

      DB[:table].range(:id) # SELECT max(id) AS v1, min(id) AS v2 FROM table LIMIT 1
      # => 1..10

[Source]

         # File lib/sequel/dataset/actions.rb, line 385
    385:     def range(column)
    386:       if r = aggregate_dataset.select{[min(column).as(v1), max(column).as(v2)]}.first
    387:         (r[:v1]..r[:v2])
    388:       end
    389:     end

select_hash(key_column, value_column)

Returns a hash with key_column values as keys and value_column values as values. Similar to to_hash, but only selects the two columns.

      DB[:table].select_hash(:id, :name) # SELECT id, name FROM table
      # => {1=>'a', 2=>'b', ...}

[Source]

         # File lib/sequel/dataset/actions.rb, line 396
    396:     def select_hash(key_column, value_column)
    397:       select(key_column, value_column).to_hash(hash_key_symbol(key_column), hash_key_symbol(value_column))
    398:     end

select_map(column=nil, &block)

Selects the column given (either as an argument or as a block), and returns an array of all values of that column in the dataset. If you give a block argument that returns an array with multiple entries, the contents of the resulting array are undefined.

      DB[:table].select_map(:id) # SELECT id FROM table
      # => [3, 5, 8, 1, ...]

      DB[:table].select_map{abs(id)} # SELECT abs(id) FROM table
      # => [3, 5, 8, 1, ...]

[Source]

         # File lib/sequel/dataset/actions.rb, line 410
    410:     def select_map(column=nil, &block)
    411:       ds = naked.ungraphed
    412:       ds = if column
    413:         raise(Error, ARG_BLOCK_ERROR_MSG) if block
    414:         ds.select(column)
    415:       else
    416:         ds.select(&block)
    417:       end
    418:       ds.map{|r| r.values.first}
    419:     end

select_order_map(column=nil, &block)

The same as select_map, but in addition orders the array by the column.

      DB[:table].select_order_map(:id) # SELECT id FROM table ORDER BY id
      # => [1, 2, 3, 4, ...]

      DB[:table].select_order_map{abs(id)} # SELECT abs(id) FROM table ORDER BY abs(id)
      # => [1, 2, 3, 4, ...]

[Source]

         # File lib/sequel/dataset/actions.rb, line 428
    428:     def select_order_map(column=nil, &block)
    429:       ds = naked.ungraphed
    430:       ds = if column
    431:         raise(Error, ARG_BLOCK_ERROR_MSG) if block
    432:         ds.select(column).order(unaliased_identifier(column))
    433:       else
    434:         ds.select(&block).order(&block)
    435:       end
    436:       ds.map{|r| r.values.first}
    437:     end

set(*args)

Alias for update, but not aliased directly so subclasses don‘t have to override both methods.

[Source]

         # File lib/sequel/dataset/actions.rb, line 441
    441:     def set(*args)
    442:       update(*args)
    443:     end

single_record()

Returns the first record in the dataset, or nil if the dataset has no records. Users should probably use `first` instead of this method.

[Source]

         # File lib/sequel/dataset/actions.rb, line 448
    448:     def single_record
    449:       clone(:limit=>1).each{|r| return r}
    450:       nil
    451:     end

single_value()

Returns the first value of the first record in the dataset. Returns nil if dataset is empty. Users should generally use `get` instead of this method.

[Source]

         # File lib/sequel/dataset/actions.rb, line 456
    456:     def single_value
    457:       if r = naked.ungraphed.single_record
    458:         r.values.first
    459:       end
    460:     end

sum(column)

Returns the sum for the given column.

      DB[:table].sum(:id) # SELECT sum(id) FROM table LIMIT 1
      # => 55

[Source]

         # File lib/sequel/dataset/actions.rb, line 466
    466:     def sum(column)
    467:       aggregate_dataset.get{sum(column)}
    468:     end

to_csv(include_column_titles = true)

Returns a string in CSV format containing the dataset records. By default the CSV representation includes the column titles in the first line. You can turn that off by passing false as the include_column_titles argument.

This does not use a CSV library or handle quoting of values in any way. If any values in any of the rows could include commas or line endings, you shouldn‘t use this.

      puts DB[:table].to_csv # SELECT * FROM table
      # id,name
      # 1,Jim
      # 2,Bob

[Source]

         # File lib/sequel/dataset/actions.rb, line 483
    483:     def to_csv(include_column_titles = true)
    484:       n = naked
    485:       cols = n.columns
    486:       csv = ''
    487:       csv << "#{cols.join(COMMA_SEPARATOR)}\r\n" if include_column_titles
    488:       n.each{|r| csv << "#{cols.collect{|c| r[c]}.join(COMMA_SEPARATOR)}\r\n"}
    489:       csv
    490:     end

to_hash(key_column, value_column = nil)

Returns a hash with one column used as key and another used as value. If rows have duplicate values for the key column, the latter row(s) will overwrite the value of the previous row(s). If the value_column is not given or nil, uses the entire hash as the value.

      DB[:table].to_hash(:id, :name) # SELECT * FROM table
      # {1=>'Jim', 2=>'Bob', ...}

      DB[:table].to_hash(:id) # SELECT * FROM table
      # {1=>{:id=>1, :name=>'Jim'}, 2=>{:id=>2, :name=>'Bob'}, ...}

[Source]

         # File lib/sequel/dataset/actions.rb, line 502
    502:     def to_hash(key_column, value_column = nil)
    503:       inject({}) do |m, r|
    504:         m[r[key_column]] = value_column ? r[value_column] : r
    505:         m
    506:       end
    507:     end

truncate()

Truncates the dataset. Returns nil.

      DB[:table].truncate # TRUNCATE table
      # => nil

[Source]

         # File lib/sequel/dataset/actions.rb, line 513
    513:     def truncate
    514:       execute_ddl(truncate_sql)
    515:     end

update(values={})

Updates values for the dataset. The returned value is generally the number of rows updated, but that is adapter dependent. `values` should a hash where the keys are columns to set and values are the values to which to set the columns.

      DB[:table].update(:x=>nil) # UPDATE table SET x = NULL
      # => 10

      DB[:table].update(:x=>:x+1, :y=>0) # UPDATE table SET x = (x + 1), :y = 0
      # => 10

[Source]

         # File lib/sequel/dataset/actions.rb, line 527
    527:     def update(values={})
    528:       execute_dui(update_sql(values))
    529:     end

## Methods that describe what the dataset supports

These methods all return booleans, with most describing whether or not the dataset supports a feature.

### Constants

WITH_SUPPORTED | = | :select_with_sql |  | Method used to check if WITH is supported

### Public Instance methods

provides_accurate_rows_matched?()

Whether this dataset will provide accurate number of rows matched for delete and update statements. Accurate in this case is the number of rows matched by the dataset‘s filter.

[Source]

        # File lib/sequel/dataset/features.rb, line 20
    20:     def provides_accurate_rows_matched?
    21:       true
    22:     end

quote_identifiers?()

Whether this dataset quotes identifiers.

[Source]

        # File lib/sequel/dataset/features.rb, line 13
    13:     def quote_identifiers?
    14:       @quote_identifiers
    15:     end

requires_sql_standard_datetimes?()

Whether the dataset requires SQL standard datetimes (false by default, as most allow strings with ISO 8601 format).

[Source]

        # File lib/sequel/dataset/features.rb, line 26
    26:     def requires_sql_standard_datetimes?
    27:       false
    28:     end

supports_cte?()

Whether the dataset supports common table expressions (the WITH clause).

[Source]

        # File lib/sequel/dataset/features.rb, line 31
    31:     def supports_cte?
    32:       select_clause_methods.include?(WITH_SUPPORTED)
    33:     end

supports_distinct_on?()

Whether the dataset supports the DISTINCT ON clause, false by default.

[Source]

        # File lib/sequel/dataset/features.rb, line 36
    36:     def supports_distinct_on?
    37:       false
    38:     end

supports_intersect_except?()

Whether the dataset supports the INTERSECT and EXCEPT compound operations, true by default.

[Source]

        # File lib/sequel/dataset/features.rb, line 41
    41:     def supports_intersect_except?
    42:       true
    43:     end

supports_intersect_except_all?()

Whether the dataset supports the INTERSECT ALL and EXCEPT ALL compound operations, true by default.

[Source]

        # File lib/sequel/dataset/features.rb, line 46
    46:     def supports_intersect_except_all?
    47:       true
    48:     end

supports_is_true?()

Whether the dataset supports the IS TRUE syntax.

[Source]

        # File lib/sequel/dataset/features.rb, line 51
    51:     def supports_is_true?
    52:       true
    53:     end

supports_join_using?()

Whether the dataset supports the JOIN table USING (column1, …) syntax.

[Source]

        # File lib/sequel/dataset/features.rb, line 56
    56:     def supports_join_using?
    57:       true
    58:     end

supports_modifying_joins?()

Whether modifying joined datasets is supported.

[Source]

        # File lib/sequel/dataset/features.rb, line 61
    61:     def supports_modifying_joins?
    62:       false
    63:     end

supports_multiple_column_in?()

Whether the IN/NOT IN operators support multiple columns when an array of values is given.

[Source]

        # File lib/sequel/dataset/features.rb, line 67
    67:     def supports_multiple_column_in?
    68:       true
    69:     end

supports_timestamp_timezones?()

Whether the dataset supports timezones in literal timestamps

[Source]

        # File lib/sequel/dataset/features.rb, line 72
    72:     def supports_timestamp_timezones?
    73:       false
    74:     end

supports_timestamp_usecs?()

Whether the dataset supports fractional seconds in literal timestamps

[Source]

        # File lib/sequel/dataset/features.rb, line 77
    77:     def supports_timestamp_usecs?
    78:       true
    79:     end

supports_window_functions?()

Whether the dataset supports window functions.

[Source]

        # File lib/sequel/dataset/features.rb, line 82
    82:     def supports_window_functions?
    83:       false
    84:     end

## Methods related to dataset graphing

Dataset graphing changes the dataset to yield hashes where keys are table name symbols and values are hashes representing the columns related to that table. All of these methods return modified copies of the receiver.

### Public Instance methods

add_graph_aliases(graph_aliases)

Adds the given graph aliases to the list of graph aliases to use, unlike `set_graph_aliases`, which replaces the list (the equivalent of `select_more` when graphing). See `set_graph_aliases`.

      DB[:table].add_graph_aliases(:some_alias=>[:table, :column])
      # SELECT ..., table.column AS some_alias
      # => {:table=>{:column=>some_alias_value, ...}, ...}

[Source]

        # File lib/sequel/dataset/graph.rb, line 17
    17:     def add_graph_aliases(graph_aliases)
    18:       columns, graph_aliases = graph_alias_columns(graph_aliases)
    19:       ds = select_more(*columns)
    20:       ds.opts[:graph_aliases] = (ds.opts[:graph_aliases] || (ds.opts[:graph][:column_aliases] rescue {}) || {}).merge(graph_aliases)
    21:       ds
    22:     end

graph(dataset, join_conditions = nil, options = {}, &block)

Allows you to join multiple datasets/tables and have the result set split into component tables.

This differs from the usual usage of join, which returns the result set as a single hash. For example:

      # CREATE TABLE artists (id INTEGER, name TEXT);
      # CREATE TABLE albums (id INTEGER, name TEXT, artist_id INTEGER);

      DB[:artists].left_outer_join(:albums, :artist_id=>:id).first
      #=> {:id=>albums.id, :name=>albums.name, :artist_id=>albums.artist_id}

      DB[:artists].graph(:albums, :artist_id=>:id).first
      #=> {:artists=>{:id=>artists.id, :name=>artists.name}, :albums=>{:id=>albums.id, :name=>albums.name, :artist_id=>albums.artist_id}}

Using a join such as left_outer_join, the attribute names that are shared between the tables are combined in the single return hash. You can get around that by using `select` with correct aliases for all of the columns, but it is simpler to use `graph` and have the result set split for you. In addition, `graph` respects any `row_proc` of the current dataset and the datasets you use with `graph`.

If you are graphing a table and all columns for that table are nil, this indicates that no matching rows existed in the table, so graph will return nil instead of a hash with all nil values:

      # If the artist doesn't have any albums
      DB[:artists].graph(:albums, :artist_id=>:id).first
      => {:artists=>{:id=>artists.id, :name=>artists.name}, :albums=>nil}

Arguments:

dataset : | Can be a symbol (specifying a table), another dataset, or an object that responds to `dataset` and returns a symbol or a dataset
join_conditions : | Any condition(s) allowed by `join_table`.
block : | A block that is passed to `join_table`.

Options:

:from_self_alias : | The alias to use when the receiver is not a graphed dataset but it contains multiple FROM tables or a JOIN. In this case, the receiver is wrapped in a from_self before graphing, and this option determines the alias to use.
:implicit_qualifier : | The qualifier of implicit conditions, see join_table.
:join_type : | The type of join to use (passed to `join_table`). Defaults to :left_outer.
:select : | An array of columns to select. When not used, selects all columns in the given dataset. When set to false, selects no columns and is like simply joining the tables, though graph keeps some metadata about the join that makes it important to use `graph` instead of `join_table`.
:table_alias : | The alias to use for the table. If not specified, doesn‘t alias the table. You will get an error if the the alias (or table) name is used more than once.

[Source]

         # File lib/sequel/dataset/graph.rb, line 74
     74:     def graph(dataset, join_conditions = nil, options = {}, &block)
     75:       # Allow the use of a model, dataset, or symbol as the first argument
     76:       # Find the table name/dataset based on the argument
     77:       dataset = dataset.dataset if dataset.respond_to?(:dataset)
     78:       table_alias = options[:table_alias]
     79:       case dataset
     80:       when Symbol
     81:         table = dataset
     82:         dataset = @db[dataset]
     83:         table_alias ||= table
     84:       when ::Sequel::Dataset
     85:         if dataset.simple_select_all?
     86:           table = dataset.opts[:from].first
     87:           table_alias ||= table
     88:         else
     89:           table = dataset
     90:           table_alias ||= dataset_alias((@opts[:num_dataset_sources] || 0)+1)
     91:         end
     92:       else
     93:         raise Error, "The dataset argument should be a symbol, dataset, or model"
     94:       end
     95:
     96:       # Raise Sequel::Error with explanation that the table alias has been used
     97:       raise_alias_error = lambda do
     98:         raise(Error, "this #{options[:table_alias] ? 'alias' : 'table'} has already been been used, please specify " \
     99:           "#{options[:table_alias] ? 'a different alias' : 'an alias via the :table_alias option'}")
    100:       end
    101:
    102:       # Only allow table aliases that haven't been used
    103:       raise_alias_error.call if @opts[:graph] && @opts[:graph][:table_aliases] && @opts[:graph][:table_aliases].include?(table_alias)
    104:
    105:       # Use a from_self if this is already a joined table
    106:       ds = (!@opts[:graph] && (@opts[:from].length > 1 || @opts[:join])) ? from_self(:alias=>options[:from_self_alias] || first_source) : self
    107:
    108:       # Join the table early in order to avoid cloning the dataset twice
    109:       ds = ds.join_table(options[:join_type] || :left_outer, table, join_conditions, :table_alias=>table_alias, :implicit_qualifier=>options[:implicit_qualifier], &block)
    110:       opts = ds.opts
    111:
    112:       # Whether to include the table in the result set
    113:       add_table = options[:select] == false ? false : true
    114:       # Whether to add the columns to the list of column aliases
    115:       add_columns = !ds.opts.include?(:graph_aliases)
    116:
    117:       # Setup the initial graph data structure if it doesn't exist
    118:       unless graph = opts[:graph]
    119:         master = alias_symbol(ds.first_source_alias)
    120:         raise_alias_error.call if master == table_alias
    121:         # Master hash storing all .graph related information
    122:         graph = opts[:graph] = {}
    123:         # Associates column aliases back to tables and columns
    124:         column_aliases = graph[:column_aliases] = {}
    125:         # Associates table alias (the master is never aliased)
    126:         table_aliases = graph[:table_aliases] = {master=>self}
    127:         # Keep track of the alias numbers used
    128:         ca_num = graph[:column_alias_num] = Hash.new(0)
    129:         # All columns in the master table are never
    130:         # aliased, but are not included if set_graph_aliases
    131:         # has been used.
    132:         if add_columns
    133:           select = opts[:select] = []
    134:           columns.each do |column|
    135:             column_aliases[column] = [master, column]
    136:             select.push(SQL::QualifiedIdentifier.new(master, column))
    137:           end
    138:         end
    139:       end
    140:
    141:       # Add the table alias to the list of aliases
    142:       # Even if it isn't been used in the result set,
    143:       # we add a key for it with a nil value so we can check if it
    144:       # is used more than once
    145:       table_aliases = graph[:table_aliases]
    146:       table_aliases[table_alias] = add_table ? dataset : nil
    147:
    148:       # Add the columns to the selection unless we are ignoring them
    149:       if add_table && add_columns
    150:         select = opts[:select]
    151:         column_aliases = graph[:column_aliases]
    152:         ca_num = graph[:column_alias_num]
    153:         # Which columns to add to the result set
    154:         cols = options[:select] || dataset.columns
    155:         # If the column hasn't been used yet, don't alias it.
    156:         # If it has been used, try table_column.
    157:         # If that has been used, try table_column_N
    158:         # using the next value of N that we know hasn't been
    159:         # used
    160:         cols.each do |column|
    161:           col_alias, identifier = if column_aliases[column]
    162:             column_alias = "#{table_alias}_#{column}""#{table_alias}_#{column}"
    163:             if column_aliases[column_alias]
    164:               column_alias_num = ca_num[column_alias]
    165:               column_alias = "#{column_alias}_#{column_alias_num}""#{column_alias}_#{column_alias_num}"
    166:               ca_num[column_alias] += 1
    167:             end
    168:             [column_alias, SQL::QualifiedIdentifier.new(table_alias, column).as(column_alias)]
    169:           else
    170:             [column, SQL::QualifiedIdentifier.new(table_alias, column)]
    171:           end
    172:           column_aliases[col_alias] = [table_alias, column]
    173:           select.push(identifier)
    174:         end
    175:       end
    176:       ds
    177:     end

set_graph_aliases(graph_aliases)

This allows you to manually specify the graph aliases to use when using graph. You can use it to only select certain columns, and have those columns mapped to specific aliases in the result set. This is the equivalent of `select` for a graphed dataset, and must be used instead of `select` whenever graphing is used.

graph_aliases : | Should be a hash with keys being symbols of column aliases, and values being either symbols or arrays with one to three elements. If the value is a symbol, it is assumed to be the same as a one element array containing that symbol. The first element of the array should be the table alias symbol. The second should be the actual column name symbol. If the array only has a single element the column name symbol will be assumed to be the same as the corresponding hash key. If the array has a third element, it is used as the value returned, instead of table_alias.column_name.

      DB[:artists].graph(:albums, :artist_id=>:id).
        set_graph_aliases(:name=>:artists,
                          :album_name=>[:albums, :name],
                          :forty_two=>[:albums, :fourtwo, 42]).first
      # SELECT artists.name, albums.name AS album_name, 42 AS forty_two ...
      # => {:artists=>{:name=>artists.name}, :albums=>{:name=>albums.name, :fourtwo=>42}}

[Source]

         # File lib/sequel/dataset/graph.rb, line 203
    203:     def set_graph_aliases(graph_aliases)
    204:       columns, graph_aliases = graph_alias_columns(graph_aliases)
    205:       ds = select(*columns)
    206:       ds.opts[:graph_aliases] = graph_aliases
    207:       ds
    208:     end

ungraphed()

Remove the splitting of results into subhashes, and all metadata related to the current graph (if any).

[Source]

         # File lib/sequel/dataset/graph.rb, line 212
    212:     def ungraphed
    213:       clone(:graph=>nil, :graph_aliases=>nil)
    214:     end

## Miscellaneous methods

These methods don‘t fit cleanly into another section.

### Constants

NOTIMPL_MSG | = | "This method must be overridden in Sequel adapters".freeze
ARRAY_ACCESS_ERROR_MSG | = | 'You cannot call Dataset#[] with an integer or with no arguments.'.freeze
ARG_BLOCK_ERROR_MSG | = | 'Must use either an argument or a block, not both'.freeze
IMPORT_ERROR_MSG | = | 'Using Sequel::Dataset#import an empty column array is not allowed'.freeze

### Attributes

db | [RW] | The database related to this dataset. This is the Database instance that will execute all of this dataset‘s queries.
opts | [RW] | The hash of options for this dataset, keys are symbols.

### Public Class methods

new(db, opts = nil)

Constructs a new Dataset instance with an associated database and options. Datasets are usually constructed by invoking the Database#[] method:

      DB[:posts]

Sequel::Dataset is an abstract class that is not useful by itself. Each database adaptor provides a subclass of Sequel::Dataset, and has the Database#dataset method return an instance of that subclass.

[Source]

        # File lib/sequel/dataset/misc.rb, line 28
    28:     def initialize(db, opts = nil)
    29:       @db = db
    30:       @quote_identifiers = db.quote_identifiers? if db.respond_to?(:quote_identifiers?)
    31:       @identifier_input_method = db.identifier_input_method if db.respond_to?(:identifier_input_method)
    32:       @identifier_output_method = db.identifier_output_method if db.respond_to?(:identifier_output_method)
    33:       @opts = opts || {}
    34:       @row_proc = nil
    35:     end

### Public Instance methods

==(o)

Define a hash value such that datasets with the same DB, opts, and SQL will be consider equal.

[Source]

        # File lib/sequel/dataset/misc.rb, line 39
    39:     def ==(o)
    40:       o.is_a?(self.class) && db == o.db  && opts == o.opts && sql == o.sql
    41:     end

as(aliaz)

Return the dataset as an aliased expression with the given alias. You can use this as a FROM or JOIN dataset, or as a column if this dataset returns a single row and column.

      DB.from(DB[:table].as(:b)) # SELECT * FROM (SELECT * FROM table) AS b

[Source]

        # File lib/sequel/dataset/misc.rb, line 53
    53:     def as(aliaz)
    54:       ::Sequel::SQL::AliasedExpression.new(self, aliaz)
    55:     end

each_server() {|server(s)}| ...}

Yield a dataset for each server in the connection pool that is tied to that server. Intended for use in sharded environments where all servers need to be modified with the same data:

      DB[:configs].where(:key=>'setting').each_server{|ds| ds.update(:value=>'new_value')}

[Source]

        # File lib/sequel/dataset/misc.rb, line 62
    62:     def each_server
    63:       db.servers.each{|s| yield server(s)}
    64:     end

eql?(o)

Alias for ==

[Source]

        # File lib/sequel/dataset/misc.rb, line 44
    44:     def eql?(o)
    45:       self == o
    46:     end

first_source()

Alias of `first_source_alias`

[Source]

        # File lib/sequel/dataset/misc.rb, line 67
    67:     def first_source
    68:       first_source_alias
    69:     end

first_source_alias()

The first source (primary table) for this dataset. If the dataset doesn‘t have a table, raises an `Error`. If the table is aliased, returns the aliased name.

      DB[:table].first_source_alias
      # => :table

      DB[:table___t].first_source_alias
      # => :t

[Source]

        # File lib/sequel/dataset/misc.rb, line 79
    79:     def first_source_alias
    80:       source = @opts[:from]
    81:       if source.nil? || source.empty?
    82:         raise Error, 'No source specified for query'
    83:       end
    84:       case s = source.first
    85:       when SQL::AliasedExpression
    86:         s.aliaz
    87:       when Symbol
    88:         sch, table, aliaz = split_symbol(s)
    89:         aliaz ? aliaz.to_sym : s
    90:       else
    91:         s
    92:       end
    93:     end

first_source_table()

The first source (primary table) for this dataset. If the dataset doesn‘t have a table, raises an error. If the table is aliased, returns the original table, not the alias

      DB[:table].first_source_alias
      # => :table

      DB[:table___t].first_source_alias
      # => :table

[Source]

         # File lib/sequel/dataset/misc.rb, line 104
    104:     def first_source_table
    105:       source = @opts[:from]
    106:       if source.nil? || source.empty?
    107:         raise Error, 'No source specified for query'
    108:       end
    109:       case s = source.first
    110:       when SQL::AliasedExpression
    111:         s.expression
    112:       when Symbol
    113:         sch, table, aliaz = split_symbol(s)
    114:         aliaz ? (sch ? SQL::QualifiedIdentifier.new(sch, table) : table.to_sym) : s
    115:       else
    116:         s
    117:       end
    118:     end

hash()

Define a hash value such that datasets with the same DB, opts, and SQL will have the same hash value

[Source]

         # File lib/sequel/dataset/misc.rb, line 122
    122:     def hash
    123:       [db, opts.sort_by{|k| k.to_s}, sql].hash
    124:     end

inspect()

Returns a string representation of the dataset including the class name and the corresponding SQL select statement.

[Source]

         # File lib/sequel/dataset/misc.rb, line 128
    128:     def inspect
    129:       "#<#{self.class}: #{sql.inspect}>"
    130:     end

split_alias(c)

Splits a possible implicit alias in C, handling both SQL::AliasedExpressions and Symbols. Returns an array of two elements, with the first being the main expression, and the second being the alias.

[Source]

         # File lib/sequel/dataset/misc.rb, line 135
    135:     def split_alias(c)
    136:       case c
    137:       when Symbol
    138:         c_table, column, aliaz = split_symbol(c)
    139:         [c_table ? SQL::QualifiedIdentifier.new(c_table, column.to_sym) : column.to_sym, aliaz]
    140:       when SQL::AliasedExpression
    141:         [c.expression, c.aliaz]
    142:       else
    143:         [c, nil]
    144:       end
    145:     end

unused_table_alias(table_alias)

Creates a unique table alias that hasn‘t already been used in the dataset. table_alias can be any type of object accepted by alias_symbol. The symbol returned will be the implicit alias in the argument, possibly appended with "_N" if the implicit alias has already been used, where N is an integer starting at 0 and increasing until an unused one is found.

      DB[:table].unused_table_alias(:t)
      # => :t

      DB[:table].unused_table_alias(:table)
      # => :table_0

      DB[:table, :table_0].unused_table_alias(:table)
      # => :table_1

[Source]

         # File lib/sequel/dataset/misc.rb, line 162
    162:     def unused_table_alias(table_alias)
    163:       table_alias = alias_symbol(table_alias)
    164:       used_aliases = []
    165:       used_aliases += opts[:from].map{|t| alias_symbol(t)} if opts[:from]
    166:       used_aliases += opts[:join].map{|j| j.table_alias ? alias_alias_symbol(j.table_alias) : alias_symbol(j.table)} if opts[:join]
    167:       if used_aliases.include?(table_alias)
    168:         i = 0
    169:         loop do
    170:           ta = "#{table_alias}_#{i}""#{table_alias}_#{i}"
    171:           return ta unless used_aliases.include?(ta)
    172:           i += 1
    173:         end
    174:       else
    175:         table_alias
    176:       end
    177:     end

## Methods related to prepared statements or bound variables

On some adapters, these use native prepared statements and bound variables, on others support is emulated. For details, see the "Prepared Statements/Bound Variables" guide.

### Classes and Modules

Module Sequel::Dataset::UnnumberedArgumentMapper

### Constants

PREPARED_ARG_PLACEHOLDER | = | LiteralString.new('?').freeze

### Public Instance methods

bind(bind_vars={})

Set the bind variables to use for the call. If bind variables have already been set for this dataset, they are updated with the contents of bind_vars.

      DB[:table].filter(:id=>:$id).bind(:id=>1).call(:first)
      # SELECT * FROM table WHERE id = ? LIMIT 1 -- (1)
      # => {:id=>1}

[Source]

         # File lib/sequel/dataset/prepared_statements.rb, line 183
    183:     def bind(bind_vars={})
    184:       clone(:bind_vars=>@opts[:bind_vars] ? @opts[:bind_vars].merge(bind_vars) : bind_vars)
    185:     end

call(type, bind_variables={}, *values, &block)

For the given type (:select, :insert, :update, or :delete), run the sql with the bind variables specified in the hash. values is a hash of passed to insert or update (if one of those types is used), which may contain placeholders.

      DB[:table].filter(:id=>:$id).call(:first, :id=>1)
      # SELECT * FROM table WHERE id = ? LIMIT 1 -- (1)
      # => {:id=>1}

[Source]

         # File lib/sequel/dataset/prepared_statements.rb, line 196
    196:     def call(type, bind_variables={}, *values, &block)
    197:       prepare(type, nil, *values).call(bind_variables, &block)
    198:     end

prepare(type, name=nil, *values)

Prepare an SQL statement for later execution. This returns a clone of the dataset extended with PreparedStatementMethods, on which you can call call with the hash of bind variables to do substitution. The prepared statement is also stored in the associated database. The following usage is identical:

      ps = DB[:table].filter(:name=>:$name).prepare(:first, :select_by_name)

      ps.call(:name=>'Blah')
      # SELECT * FROM table WHERE name = ? -- ('Blah')
      # => {:id=>1, :name=>'Blah'}

      DB.call(:select_by_name, :name=>'Blah') # Same thing

[Source]

         # File lib/sequel/dataset/prepared_statements.rb, line 213
    213:     def prepare(type, name=nil, *values)
    214:       ps = to_prepared_statement(type, values)
    215:       db.prepared_statements[name] = ps if name
    216:       ps
    217:     end

### Protected Instance methods

to_prepared_statement(type, values=nil)

Return a cloned copy of the current dataset extended with PreparedStatementMethods, setting the type and modify values.

[Source]

         # File lib/sequel/dataset/prepared_statements.rb, line 223
    223:     def to_prepared_statement(type, values=nil)
    224:       ps = bind
    225:       ps.extend(PreparedStatementMethods)
    226:       ps.prepared_type = type
    227:       ps.prepared_modify_values = values
    228:       ps
    229:     end

## Methods that return modified datasets

These methods all return modified copies of the receiver.

### Constants

COLUMN_CHANGE_OPTS | = | [:select, :sql, :from, :join].freeze |  | The dataset options that require the removal of cached columns if changed.
NON_SQL_OPTIONS | = | [:server, :defaults, :overrides, :graph, :eager_graph, :graph_aliases] |  | Which options don‘t affect the SQL generation. Used by simple_select_all? to determine if this is a simple SELECT * FROM table.
CONDITIONED_JOIN_TYPES | = | [:inner, :full_outer, :right_outer, :left_outer, :full, :right, :left] |  | These symbols have _join methods created (e.g. inner_join) that call join_table with the symbol, passing along the arguments and block from the method call.
UNCONDITIONED_JOIN_TYPES | = | [:natural, :natural_left, :natural_right, :natural_full, :cross] |  | These symbols have _join methods created (e.g. natural_join) that call join_table with the symbol. They only accept a single table argument which is passed to join_table, and they raise an error if called with a block.
JOIN_METHODS | = | (CONDITIONED_JOIN_TYPES + UNCONDITIONED_JOIN_TYPES).map{|x| "#{x}_join".to_sym} + [:join, :join_table] |  | All methods that return modified datasets with a joined table added.
QUERY_METHODS | = | %w'add_graph_aliases and distinct except exclude filter for_update from from_self graph grep group group_and_count group_by having intersect invert limit lock_style naked or order order_append order_by order_more order_prepend paginate qualify query reverse reverse_order select select_all select_append select_more server set_defaults set_graph_aliases set_overrides unfiltered ungraphed ungrouped union unlimited unordered where with with_recursive with_sql'.collect{|x| x.to_sym} + JOIN_METHODS |  | Methods that return modified datasets

### Public Instance methods

and(*cond, &block)

Adds an further filter to an existing filter using AND. If no filter exists an error is raised. This method is identical to filter except it expects an existing filter.

      DB[:table].filter(:a).and(:b) # SELECT * FROM table WHERE a AND b

[Source]

        # File lib/sequel/dataset/query.rb, line 43
    43:     def and(*cond, &block)
    44:       raise(InvalidOperation, "No existing filter found.") unless @opts[:having] || @opts[:where]
    45:       filter(*cond, &block)
    46:     end

clone(opts = {})

Returns a new clone of the dataset with with the given options merged. If the options changed include options in COLUMN_CHANGE_OPTS, the cached columns are deleted. This method should generally not be called directly by user code.

[Source]

        # File lib/sequel/dataset/query.rb, line 52
    52:     def clone(opts = {})
    53:       c = super()
    54:       c.opts = @opts.merge(opts)
    55:       c.instance_variable_set(:@columns, nil) if opts.keys.any?{|o| COLUMN_CHANGE_OPTS.include?(o)}
    56:       c
    57:     end

distinct(*args)

Returns a copy of the dataset with the SQL DISTINCT clause. The DISTINCT clause is used to remove duplicate rows from the output. If arguments are provided, uses a DISTINCT ON clause, in which case it will only be distinct on those columns, instead of all returned columns. Raises an error if arguments are given and DISTINCT ON is not supported.

     DB[:items].distinct # SQL: SELECT DISTINCT * FROM items
     DB[:items].order(:id).distinct(:id) # SQL: SELECT DISTINCT ON (id) * FROM items ORDER BY id

[Source]

        # File lib/sequel/dataset/query.rb, line 68
    68:     def distinct(*args)
    69:       raise(InvalidOperation, "DISTINCT ON not supported") if !args.empty? && !supports_distinct_on?
    70:       clone(:distinct => args)
    71:     end

except(dataset, opts={})

Adds an EXCEPT clause using a second dataset object. An EXCEPT compound dataset returns all rows in the current dataset that are not in the given dataset. Raises an `InvalidOperation` if the operation is not supported. Options:

:alias : | Use the given value as the from_self alias
:all : | Set to true to use EXCEPT ALL instead of EXCEPT, so duplicate rows can occur
:from_self : | Set to false to not wrap the returned dataset in a from_self, use with care.

      DB[:items].except(DB[:other_items])
      # SELECT * FROM items EXCEPT SELECT * FROM other_items

      DB[:items].except(DB[:other_items], :all=>true, :from_self=>false)
      # SELECT * FROM items EXCEPT ALL SELECT * FROM other_items

      DB[:items].except(DB[:other_items], :alias=>:i)
      # SELECT * FROM (SELECT * FROM items EXCEPT SELECT * FROM other_items) AS i

[Source]

        # File lib/sequel/dataset/query.rb, line 90
    90:     def except(dataset, opts={})
    91:       opts = {:all=>opts} unless opts.is_a?(Hash)
    92:       raise(InvalidOperation, "EXCEPT not supported") unless supports_intersect_except?
    93:       raise(InvalidOperation, "EXCEPT ALL not supported") if opts[:all] && !supports_intersect_except_all?
    94:       compound_clone(:except, dataset, opts)
    95:     end

exclude(*cond, &block)

Performs the inverse of Dataset#filter. Note that if you have multiple filter conditions, this is not the same as a negation of all conditions.

      DB[:items].exclude(:category => 'software')
      # SELECT * FROM items WHERE (category != 'software')

      DB[:items].exclude(:category => 'software', :id=>3)
      # SELECT * FROM items WHERE ((category != 'software') OR (id != 3))

[Source]

         # File lib/sequel/dataset/query.rb, line 105
    105:     def exclude(*cond, &block)
    106:       clause = (@opts[:having] ? :having : :where)
    107:       cond = cond.first if cond.size == 1
    108:       cond = filter_expr(cond, &block)
    109:       cond = SQL::BooleanExpression.invert(cond)
    110:       cond = SQL::BooleanExpression.new(:AND, @opts[clause], cond) if @opts[clause]
    111:       clone(clause => cond)
    112:     end

filter(*cond, &block)

Returns a copy of the dataset with the given conditions imposed upon it. If the query already has a HAVING clause, then the conditions are imposed in the HAVING clause. If not, then they are imposed in the WHERE clause.

filter accepts the following argument types:

- Hash - list of equality/inclusion expressions
- Array - depends:
  - If first member is a string, assumes the rest of the arguments are parameters and interpolates them into the string.
  - If all members are arrays of length two, treats the same way as a hash, except it allows for duplicate keys to be specified.
  - Otherwise, treats each argument as a separate condition.
- String - taken literally
- Symbol - taken as a boolean column argument (e.g. WHERE active)
- Sequel::SQL::BooleanExpression - an existing condition expression, probably created using the Sequel expression filter DSL.

filter also takes a block, which should return one of the above argument types, and is treated the same way. This block yields a virtual row object, which is easy to use to create identifiers and functions. For more details on the virtual row support, see the "Virtual Rows" guide

If both a block and regular argument are provided, they get ANDed together.

Examples:

      DB[:items].filter(:id => 3)
      # SELECT * FROM items WHERE (id = 3)

      DB[:items].filter('price < ?', 100)
      # SELECT * FROM items WHERE price < 100

      DB[:items].filter([[:id, (1,2,3)], [:id, 0..10]])
      # SELECT * FROM items WHERE ((id IN (1, 2, 3)) AND ((id >= 0) AND (id <= 10)))

      DB[:items].filter('price < 100')
      # SELECT * FROM items WHERE price < 100

      DB[:items].filter(:active)
      # SELECT * FROM items WHERE :active

      DB[:items].filter{price < 100}
      # SELECT * FROM items WHERE (price < 100)

Multiple filter calls can be chained for scoping:

      software = dataset.filter(:category => 'software').filter{price < 100}
      # SELECT * FROM items WHERE ((category = 'software') AND (price < 100))

See the the "Dataset Filtering" guide for more examples and details.

[Source]

         # File lib/sequel/dataset/query.rb, line 166
    166:     def filter(*cond, &block)
    167:       _filter(@opts[:having] ? :having : :where, *cond, &block)
    168:     end

for_update()

Returns a cloned dataset with a :update lock style.

      DB[:table].for_update # SELECT * FROM table FOR UPDATE

[Source]

         # File lib/sequel/dataset/query.rb, line 173
    173:     def for_update
    174:       lock_style(:update)
    175:     end

from(*source)

Returns a copy of the dataset with the source changed. If no source is given, removes all tables. If multiple sources are given, it is the same as using a CROSS JOIN (cartesian product) between all tables.

      DB[:items].from # SQL: SELECT *
      DB[:items].from(:blah) # SQL: SELECT * FROM blah
      DB[:items].from(:blah, :foo) # SQL: SELECT * FROM blah, foo

[Source]

         # File lib/sequel/dataset/query.rb, line 184
    184:     def from(*source)
    185:       table_alias_num = 0
    186:       sources = []
    187:       source.each do |s|
    188:         case s
    189:         when Hash
    190:           s.each{|k,v| sources << SQL::AliasedExpression.new(k,v)}
    191:         when Dataset
    192:           sources << SQL::AliasedExpression.new(s, dataset_alias(table_alias_num+=1))
    193:         when Symbol
    194:           sch, table, aliaz = split_symbol(s)
    195:           if aliaz
    196:             s = sch ? SQL::QualifiedIdentifier.new(sch.to_sym, table.to_sym) : SQL::Identifier.new(table.to_sym)
    197:             sources << SQL::AliasedExpression.new(s, aliaz.to_sym)
    198:           else
    199:             sources << s
    200:           end
    201:         else
    202:           sources << s
    203:         end
    204:       end
    205:       o = {:from=>sources.empty? ? nil : sources}
    206:       o[:num_dataset_sources] = table_alias_num if table_alias_num > 0
    207:       clone(o)
    208:     end

from_self(opts={})

Returns a dataset selecting from the current dataset. Supplying the :alias option controls the alias of the result.

      ds = DB[:items].order(:name).select(:id, :name)
      # SELECT id,name FROM items ORDER BY name

      ds.from_self
      # SELECT * FROM (SELECT id, name FROM items ORDER BY name) AS t1

      ds.from_self(:alias=>:foo)
      # SELECT * FROM (SELECT id, name FROM items ORDER BY name) AS foo

[Source]

         # File lib/sequel/dataset/query.rb, line 221
    221:     def from_self(opts={})
    222:       fs = {}
    223:       @opts.keys.each{|k| fs[k] = nil unless NON_SQL_OPTIONS.include?(k)}
    224:       clone(fs).from(opts[:alias] ? as(opts[:alias]) : self)
    225:     end

grep(columns, patterns, opts={})

Match any of the columns to any of the patterns. The terms can be strings (which use LIKE) or regular expressions (which are only supported on MySQL and PostgreSQL). Note that the total number of pattern matches will be Array(columns).length * Array(terms).length, which could cause performance issues.

Options (all are boolean):

:all_columns : | All columns must be matched to any of the given patterns.
:all_patterns : | All patterns must match at least one of the columns.
:case_insensitive : | Use a case insensitive pattern match (the default is case sensitive if the database supports it).

If both :all_columns and :all_patterns are true, all columns must match all patterns.

Examples:

      dataset.grep(:a, '%test%')
      # SELECT * FROM items WHERE (a LIKE '%test%')

      dataset.grep([:a, :b], %w'%test% foo')
      # SELECT * FROM items WHERE ((a LIKE '%test%') OR (a LIKE 'foo') OR (b LIKE '%test%') OR (b LIKE 'foo'))

      dataset.grep([:a, :b], %w'%foo% %bar%', :all_patterns=>true)
      # SELECT * FROM a WHERE (((a LIKE '%foo%') OR (b LIKE '%foo%')) AND ((a LIKE '%bar%') OR (b LIKE '%bar%')))

      dataset.grep([:a, :b], %w'%foo% %bar%', :all_columns=>true)
      # SELECT * FROM a WHERE (((a LIKE '%foo%') OR (a LIKE '%bar%')) AND ((b LIKE '%foo%') OR (b LIKE '%bar%')))

      dataset.grep([:a, :b], %w'%foo% %bar%', :all_patterns=>true, :all_columns=>true)
      # SELECT * FROM a WHERE ((a LIKE '%foo%') AND (b LIKE '%foo%') AND (a LIKE '%bar%') AND (b LIKE '%bar%'))

[Source]

         # File lib/sequel/dataset/query.rb, line 258
    258:     def grep(columns, patterns, opts={})
    259:       if opts[:all_patterns]
    260:         conds = Array(patterns).map do |pat|
    261:           SQL::BooleanExpression.new(opts[:all_columns] ? :AND : :OR, *Array(columns).map{|c| SQL::StringExpression.like(c, pat, opts)})
    262:         end
    263:         filter(SQL::BooleanExpression.new(opts[:all_patterns] ? :AND : :OR, *conds))
    264:       else
    265:         conds = Array(columns).map do |c|
    266:           SQL::BooleanExpression.new(:OR, *Array(patterns).map{|pat| SQL::StringExpression.like(c, pat, opts)})
    267:         end
    268:         filter(SQL::BooleanExpression.new(opts[:all_columns] ? :AND : :OR, *conds))
    269:       end
    270:     end

group(*columns)

Returns a copy of the dataset with the results grouped by the value of the given columns.

      DB[:items].group(:id) # SELECT * FROM items GROUP BY id
      DB[:items].group(:id, :name) # SELECT * FROM items GROUP BY id, name

[Source]

         # File lib/sequel/dataset/query.rb, line 277
    277:     def group(*columns)
    278:       clone(:group => (columns.compact.empty? ? nil : columns))
    279:     end

group_and_count(*columns)

Returns a dataset grouped by the given column with count by group. Column aliases may be supplied, and will be included in the select clause.

Examples:

      DB[:items].group_and_count(:name).all
      # SELECT name, count(*) AS count FROM items GROUP BY name
      # => [{:name=>'a', :count=>1}, ...]

      DB[:items].group_and_count(:first_name, :last_name).all
      # SELECT first_name, last_name, count(*) AS count FROM items GROUP BY first_name, last_name
      # => [{:first_name=>'a', :last_name=>'b', :count=>1}, ...]

      DB[:items].group_and_count(:first_name___name).all
      # SELECT first_name AS name, count(*) AS count FROM items GROUP BY first_name
      # => [{:name=>'a', :count=>1}, ...]

[Source]

         # File lib/sequel/dataset/query.rb, line 302
    302:     def group_and_count(*columns)
    303:       group(*columns.map{|c| unaliased_identifier(c)}).select(*(columns + [COUNT_OF_ALL_AS_COUNT]))
    304:     end

group_by(*columns)

Alias of group

[Source]

         # File lib/sequel/dataset/query.rb, line 282
    282:     def group_by(*columns)
    283:       group(*columns)
    284:     end

having(*cond, &block)

Returns a copy of the dataset with the HAVING conditions changed. See filter for argument types.

      DB[:items].group(:sum).having(:sum=>10)
      # SELECT * FROM items GROUP BY sum HAVING (sum = 10)

[Source]

         # File lib/sequel/dataset/query.rb, line 310
    310:     def having(*cond, &block)
    311:       _filter(:having, *cond, &block)
    312:     end

intersect(dataset, opts={})

Adds an INTERSECT clause using a second dataset object. An INTERSECT compound dataset returns all rows in both the current dataset and the given dataset. Raises an `InvalidOperation` if the operation is not supported. Options:

:alias : | Use the given value as the from_self alias
:all : | Set to true to use INTERSECT ALL instead of INTERSECT, so duplicate rows can occur
:from_self : | Set to false to not wrap the returned dataset in a from_self, use with care.

      DB[:items].intersect(DB[:other_items])
      # SELECT * FROM (SELECT * FROM items INTERSECT SELECT * FROM other_items) AS t1

      DB[:items].intersect(DB[:other_items], :all=>true, :from_self=>false)
      # SELECT * FROM items INTERSECT ALL SELECT * FROM other_items

      DB[:items].intersect(DB[:other_items], :alias=>:i)
      # SELECT * FROM (SELECT * FROM items INTERSECT SELECT * FROM other_items) AS i

[Source]

         # File lib/sequel/dataset/query.rb, line 331
    331:     def intersect(dataset, opts={})
    332:       opts = {:all=>opts} unless opts.is_a?(Hash)
    333:       raise(InvalidOperation, "INTERSECT not supported") unless supports_intersect_except?
    334:       raise(InvalidOperation, "INTERSECT ALL not supported") if opts[:all] && !supports_intersect_except_all?
    335:       compound_clone(:intersect, dataset, opts)
    336:     end

invert()

Inverts the current filter.

      DB[:items].filter(:category => 'software').invert
      # SELECT * FROM items WHERE (category != 'software')

      DB[:items].filter(:category => 'software', :id=>3).invert
      # SELECT * FROM items WHERE ((category != 'software') OR (id != 3))

[Source]

         # File lib/sequel/dataset/query.rb, line 345
    345:     def invert
    346:       having, where = @opts[:having], @opts[:where]
    347:       raise(Error, "No current filter") unless having || where
    348:       o = {}
    349:       o[:having] = SQL::BooleanExpression.invert(having) if having
    350:       o[:where] = SQL::BooleanExpression.invert(where) if where
    351:       clone(o)
    352:     end

join(*args, &block)

Alias of `inner_join`

[Source]

         # File lib/sequel/dataset/query.rb, line 355
    355:     def join(*args, &block)
    356:       inner_join(*args, &block)
    357:     end

join_table(type, table, expr=nil, options={}) {|table_name, last_alias, @opts[:join] || []| ...}

Returns a joined dataset. Uses the following arguments:

- type - The type of join to do (e.g. :inner)
- table - Depends on type:
  - Dataset - a subselect is performed with an alias of tN for some value of N
  - Model (or anything responding to :table_name) - table.table_name
  - String, Symbol: table
- expr - specifies conditions, depends on type:
  - Hash, Array of two element arrays - Assumes key (1st arg) is column of joined table (unless already qualified), and value (2nd arg) is column of the last joined or primary table (or the :implicit_qualifier option). To specify multiple conditions on a single joined table column, you must use an array. Uses a JOIN with an ON clause.
  - Array - If all members of the array are symbols, considers them as columns and uses a JOIN with a USING clause. Most databases will remove duplicate columns from the result set if this is used.
  - nil - If a block is not given, doesn‘t use ON or USING, so the JOIN should be a NATURAL or CROSS join. If a block is given, uses an ON clause based on the block, see below.
  - Everything else - pretty much the same as a using the argument in a call to filter, so strings are considered literal, symbols specify boolean columns, and Sequel expressions can be used. Uses a JOIN with an ON clause.
- options - a hash of options, with any of the following keys:
  - :table_alias - the name of the table‘s alias when joining, necessary for joining to the same table more than once. No alias is used by default.
  - :implicit_qualifier - The name to use for qualifying implicit conditions. By default, the last joined or primary table is used.
- block - The block argument should only be given if a JOIN with an ON clause is used, in which case it yields the table alias/name for the table currently being joined, the table alias/name for the last joined (or first table), and an array of previous SQL::JoinClause. Unlike `filter`, this block is not treated as a virtual row block.

[Source]

         # File lib/sequel/dataset/query.rb, line 389
    389:     def join_table(type, table, expr=nil, options={}, &block)
    390:       using_join = expr.is_a?(Array) && !expr.empty? && expr.all?{|x| x.is_a?(Symbol)}
    391:       if using_join && !supports_join_using?
    392:         h = {}
    393:         expr.each{|s| h[s] = s}
    394:         return join_table(type, table, h, options)
    395:       end
    396:
    397:       case options
    398:       when Hash
    399:         table_alias = options[:table_alias]
    400:         last_alias = options[:implicit_qualifier]
    401:       when Symbol, String, SQL::Identifier
    402:         table_alias = options
    403:         last_alias = nil
    404:       else
    405:         raise Error, "invalid options format for join_table: #{options.inspect}"
    406:       end
    407:
    408:       if Dataset === table
    409:         if table_alias.nil?
    410:           table_alias_num = (@opts[:num_dataset_sources] || 0) + 1
    411:           table_alias = dataset_alias(table_alias_num)
    412:         end
    413:         table_name = table_alias
    414:       else
    415:         table = table.table_name if table.respond_to?(:table_name)
    416:         table, implicit_table_alias = split_alias(table)
    417:         table_alias ||= implicit_table_alias
    418:         table_name = table_alias || table
    419:       end
    420:
    421:       join = if expr.nil? and !block
    422:         SQL::JoinClause.new(type, table, table_alias)
    423:       elsif using_join
    424:         raise(Sequel::Error, "can't use a block if providing an array of symbols as expr") if block
    425:         SQL::JoinUsingClause.new(expr, type, table, table_alias)
    426:       else
    427:         last_alias ||= @opts[:last_joined_table] || first_source_alias
    428:         if Sequel.condition_specifier?(expr)
    429:           expr = expr.collect do |k, v|
    430:             k = qualified_column_name(k, table_name) if k.is_a?(Symbol)
    431:             v = qualified_column_name(v, last_alias) if v.is_a?(Symbol)
    432:             [k,v]
    433:           end
    434:         end
    435:         if block
    436:           expr2 = yield(table_name, last_alias, @opts[:join] || [])
    437:           expr = expr ? SQL::BooleanExpression.new(:AND, expr, expr2) : expr2
    438:         end
    439:         SQL::JoinOnClause.new(expr, type, table, table_alias)
    440:       end
    441:
    442:       opts = {:join => (@opts[:join] || []) + [join], :last_joined_table => table_name}
    443:       opts[:num_dataset_sources] = table_alias_num if table_alias_num
    444:       clone(opts)
    445:     end

limit(l, o = nil)

If given an integer, the dataset will contain only the first l results. If given a range, it will contain only those at offsets within that range. If a second argument is given, it is used as an offset. To use an offset without a limit, pass nil as the first argument.

      DB[:items].limit(10) # SELECT * FROM items LIMIT 10
      DB[:items].limit(10, 20) # SELECT * FROM items LIMIT 10 OFFSET 20
      DB[:items].limit(10...20) # SELECT * FROM items LIMIT 10 OFFSET 10
      DB[:items].limit(10..20) # SELECT * FROM items LIMIT 11 OFFSET 10
      DB[:items].limit(nil, 20) # SELECT * FROM items OFFSET 20

[Source]

         # File lib/sequel/dataset/query.rb, line 464
    464:     def limit(l, o = nil)
    465:       return from_self.limit(l, o) if @opts[:sql]
    466:
    467:       if Range === l
    468:         o = l.first
    469:         l = l.last - l.first + (l.exclude_end? ? 0 : 1)
    470:       end
    471:       l = l.to_i if l.is_a?(String) && !l.is_a?(LiteralString)
    472:       if l.is_a?(Integer)
    473:         raise(Error, 'Limits must be greater than or equal to 1') unless l >= 1
    474:       end
    475:       opts = {:limit => l}
    476:       if o
    477:         o = o.to_i if o.is_a?(String) && !o.is_a?(LiteralString)
    478:         if o.is_a?(Integer)
    479:           raise(Error, 'Offsets must be greater than or equal to 0') unless o >= 0
    480:         end
    481:         opts[:offset] = o
    482:       end
    483:       clone(opts)
    484:     end

lock_style(style)

Returns a cloned dataset with the given lock style. If style is a string, it will be used directly. Otherwise, a symbol may be used for database independent locking. Currently :update is respected by most databases, and :share is supported by some.

      DB[:items].lock_style('FOR SHARE') # SELECT * FROM items FOR SHARE

[Source]

         # File lib/sequel/dataset/query.rb, line 492
    492:     def lock_style(style)
    493:       clone(:lock => style)
    494:     end

naked()

Returns a cloned dataset without a row_proc.

      ds = DB[:items]
      ds.row_proc = proc{|r| r.invert}
      ds.all # => [{2=>:id}]
      ds.naked.all # => [{:id=>2}]

[Source]

         # File lib/sequel/dataset/query.rb, line 502
    502:     def naked
    503:       ds = clone
    504:       ds.row_proc = nil
    505:       ds
    506:     end

or(*cond, &block)

Adds an alternate filter to an existing filter using OR. If no filter exists an `Error` is raised.

      DB[:items].filter(:a).or(:b) # SELECT * FROM items WHERE a OR b

[Source]

         # File lib/sequel/dataset/query.rb, line 512
    512:     def or(*cond, &block)
    513:       clause = (@opts[:having] ? :having : :where)
    514:       raise(InvalidOperation, "No existing filter found.") unless @opts[clause]
    515:       cond = cond.first if cond.size == 1
    516:       clone(clause => SQL::BooleanExpression.new(:OR, @opts[clause], filter_expr(cond, &block)))
    517:     end

order(*columns, &block)

Returns a copy of the dataset with the order changed. If the dataset has an existing order, it is ignored and overwritten with this order. If a nil is given the returned dataset has no order. This can accept multiple arguments of varying kinds, such as SQL functions. If a block is given, it is treated as a virtual row block, similar to `filter`.

      DB[:items].order(:name) # SELECT * FROM items ORDER BY name
      DB[:items].order(:a, :b) # SELECT * FROM items ORDER BY a, b
      DB[:items].order('a + b'.lit) # SELECT * FROM items ORDER BY a + b
      DB[:items].order(:a + :b) # SELECT * FROM items ORDER BY (a + b)
      DB[:items].order(:name.desc) # SELECT * FROM items ORDER BY name DESC
      DB[:items].order(:name.asc(:nulls=>:last)) # SELECT * FROM items ORDER BY name ASC NULLS LAST
      DB[:items].order{sum(name).desc} # SELECT * FROM items ORDER BY sum(name) DESC
      DB[:items].order(nil) # SELECT * FROM items

[Source]

         # File lib/sequel/dataset/query.rb, line 533
    533:     def order(*columns, &block)
    534:       columns += Array(Sequel.virtual_row(&block)) if block
    535:       clone(:order => (columns.compact.empty?) ? nil : columns)
    536:     end

order_append(*columns, &block)

Alias of order_more, for naming consistency with order_prepend.

[Source]

         # File lib/sequel/dataset/query.rb, line 539
    539:     def order_append(*columns, &block)
    540:       order_more(*columns, &block)
    541:     end

order_by(*columns, &block)

Alias of order

[Source]

         # File lib/sequel/dataset/query.rb, line 544
    544:     def order_by(*columns, &block)
    545:       order(*columns, &block)
    546:     end

order_more(*columns, &block)

Returns a copy of the dataset with the order columns added to the end of the existing order.

      DB[:items].order(:a).order(:b) # SELECT * FROM items ORDER BY b
      DB[:items].order(:a).order_more(:b) # SELECT * FROM items ORDER BY a, b

[Source]

         # File lib/sequel/dataset/query.rb, line 553
    553:     def order_more(*columns, &block)
    554:       columns = @opts[:order] + columns if @opts[:order]
    555:       order(*columns, &block)
    556:     end

order_prepend(*columns, &block)

Returns a copy of the dataset with the order columns added to the beginning of the existing order.

      DB[:items].order(:a).order(:b) # SELECT * FROM items ORDER BY b
      DB[:items].order(:a).order_prepend(:b) # SELECT * FROM items ORDER BY b, a

[Source]

         # File lib/sequel/dataset/query.rb, line 563
    563:     def order_prepend(*columns, &block)
    564:       ds = order(*columns, &block)
    565:       @opts[:order] ? ds.order_more(*@opts[:order]) : ds
    566:     end

qualify(table=first_source)

Qualify to the given table, or first source if not table is given.

      DB[:items].filter(:id=>1).qualify
      # SELECT items.* FROM items WHERE (items.id = 1)

      DB[:items].filter(:id=>1).qualify(:i)
      # SELECT i.* FROM items WHERE (i.id = 1)

[Source]

         # File lib/sequel/dataset/query.rb, line 575
    575:     def qualify(table=first_source)
    576:       qualify_to(table)
    577:     end

qualify_to(table)

Return a copy of the dataset with unqualified identifiers in the SELECT, WHERE, GROUP, HAVING, and ORDER clauses qualified by the given table. If no columns are currently selected, select all columns of the given table.

      DB[:items].filter(:id=>1).qualify_to(:i)
      # SELECT i.* FROM items WHERE (i.id = 1)

[Source]

         # File lib/sequel/dataset/query.rb, line 586
    586:     def qualify_to(table)
    587:       o = @opts
    588:       return clone if o[:sql]
    589:       h = {}
    590:       (o.keys & QUALIFY_KEYS).each do |k|
    591:         h[k] = qualified_expression(o[k], table)
    592:       end
    593:       h[:select] = [SQL::ColumnAll.new(table)] if !o[:select] || o[:select].empty?
    594:       clone(h)
    595:     end

qualify_to_first_source()

Qualify the dataset to its current first source. This is useful if you have unqualified identifiers in the query that all refer to the first source, and you want to join to another table which has columns with the same name as columns in the current dataset. See `qualify_to`.

      DB[:items].filter(:id=>1).qualify_to_first_source
      # SELECT items.* FROM items WHERE (items.id = 1)

[Source]

         # File lib/sequel/dataset/query.rb, line 605
    605:     def qualify_to_first_source
    606:       qualify_to(first_source)
    607:     end

reverse(*order)

Returns a copy of the dataset with the order reversed. If no order is given, the existing order is inverted.

      DB[:items].reverse(:id) # SELECT * FROM items ORDER BY id DESC
      DB[:items].order(:id).reverse # SELECT * FROM items ORDER BY id DESC
      DB[:items].order(:id).reverse(:name.asc) # SELECT * FROM items ORDER BY name ASC

[Source]

         # File lib/sequel/dataset/query.rb, line 615
    615:     def reverse(*order)
    616:       order(*invert_order(order.empty? ? @opts[:order] : order))
    617:     end

reverse_order(*order)

Alias of `reverse`

[Source]

         # File lib/sequel/dataset/query.rb, line 620
    620:     def reverse_order(*order)
    621:       reverse(*order)
    622:     end

select(*columns, &block)

Returns a copy of the dataset with the columns selected changed to the given columns. This also takes a virtual row block, similar to `filter`.

      DB[:items].select(:a) # SELECT a FROM items
      DB[:items].select(:a, :b) # SELECT a, b FROM items
      DB[:items].select{[a, sum(b)]} # SELECT a, sum(b) FROM items

[Source]

         # File lib/sequel/dataset/query.rb, line 631
    631:     def select(*columns, &block)
    632:       columns += Array(Sequel.virtual_row(&block)) if block
    633:       m = []
    634:       columns.each do |i|
    635:         i.is_a?(Hash) ? m.concat(i.map{|k, v| SQL::AliasedExpression.new(k,v)}) : m << i
    636:       end
    637:       clone(:select => m)
    638:     end

select_all()

Returns a copy of the dataset selecting the wildcard.

      DB[:items].select(:a).select_all # SELECT * FROM items

[Source]

         # File lib/sequel/dataset/query.rb, line 643
    643:     def select_all
    644:       clone(:select => nil)
    645:     end

select_append(*columns, &block)

Returns a copy of the dataset with the given columns added to the existing selected columns. If no columns are currently selected, it will select the columns given in addition to *.

      DB[:items].select(:a).select(:b) # SELECT b FROM items
      DB[:items].select(:a).select_append(:b) # SELECT a, b FROM items
      DB[:items].select_append(:b) # SELECT *, b FROM items

[Source]

         # File lib/sequel/dataset/query.rb, line 654
    654:     def select_append(*columns, &block)
    655:       cur_sel = @opts[:select]
    656:       cur_sel = [WILDCARD] if !cur_sel || cur_sel.empty?
    657:       select(*(cur_sel + columns), &block)
    658:     end

select_more(*columns, &block)

Returns a copy of the dataset with the given columns added to the existing selected columns. If no columns are currently selected it will just select the columns given.

      DB[:items].select(:a).select(:b) # SELECT b FROM items
      DB[:items].select(:a).select_more(:b) # SELECT a, b FROM items
      DB[:items].select_more(:b) # SELECT b FROM items

[Source]

         # File lib/sequel/dataset/query.rb, line 667
    667:     def select_more(*columns, &block)
    668:       columns = @opts[:select] + columns if @opts[:select]
    669:       select(*columns, &block)
    670:     end

server(servr)

Set the server for this dataset to use. Used to pick a specific database shard to run a query against, or to override the default (which is SELECT uses :read_only database and all other queries use the :default database). This method is always available but is only useful when database sharding is being used.

      DB[:items].all # Uses the :read_only or :default server
      DB[:items].delete # Uses the :default server
      DB[:items].server(:blah).delete # Uses the :blah server

[Source]

         # File lib/sequel/dataset/query.rb, line 681
    681:     def server(servr)
    682:       clone(:server=>servr)
    683:     end

set_defaults(hash)

Set the default values for insert and update statements. The values hash passed to insert or update are merged into this hash, so any values in the hash passed to insert or update will override values passed to this method.

      DB[:items].set_defaults(:a=>'a', :c=>'c').insert(:a=>'d', :b=>'b')
      # INSERT INTO items (a, c, b) VALUES ('d', 'c', 'b')

[Source]

         # File lib/sequel/dataset/query.rb, line 691
    691:     def set_defaults(hash)
    692:       clone(:defaults=>(@opts[:defaults]||{}).merge(hash))
    693:     end

set_overrides(hash)

Set values that override hash arguments given to insert and update statements. This hash is merged into the hash provided to insert or update, so values will override any values given in the insert/update hashes.

      DB[:items].set_overrides(:a=>'a', :c=>'c').insert(:a=>'d', :b=>'b')
      # INSERT INTO items (a, c, b) VALUES ('a', 'c', 'b')

[Source]

         # File lib/sequel/dataset/query.rb, line 701
    701:     def set_overrides(hash)
    702:       clone(:overrides=>hash.merge(@opts[:overrides]||{}))
    703:     end

unfiltered()

Returns a copy of the dataset with no filters (HAVING or WHERE clause) applied.

      DB[:items].group(:a).having(:a=>1).where(:b).unfiltered
      # SELECT * FROM items GROUP BY a

[Source]

         # File lib/sequel/dataset/query.rb, line 709
    709:     def unfiltered
    710:       clone(:where => nil, :having => nil)
    711:     end

ungrouped()

Returns a copy of the dataset with no grouping (GROUP or HAVING clause) applied.

      DB[:items].group(:a).having(:a=>1).where(:b).ungrouped
      # SELECT * FROM items WHERE b

[Source]

         # File lib/sequel/dataset/query.rb, line 717
    717:     def ungrouped
    718:       clone(:group => nil, :having => nil)
    719:     end

union(dataset, opts={})

Adds a UNION clause using a second dataset object. A UNION compound dataset returns all rows in either the current dataset or the given dataset. Options:

:alias : | Use the given value as the from_self alias
:all : | Set to true to use UNION ALL instead of UNION, so duplicate rows can occur
:from_self : | Set to false to not wrap the returned dataset in a from_self, use with care.

      DB[:items].union(DB[:other_items]).sql
      #=> "SELECT * FROM items UNION SELECT * FROM other_items"

      DB[:items].union(DB[:other_items], :all=>true, :from_self=>false)
      # SELECT * FROM items UNION ALL SELECT * FROM other_items

      DB[:items].union(DB[:other_items], :alias=>:i)
      # SELECT * FROM (SELECT * FROM items UNION SELECT * FROM other_items) AS i

[Source]

         # File lib/sequel/dataset/query.rb, line 737
    737:     def union(dataset, opts={})
    738:       opts = {:all=>opts} unless opts.is_a?(Hash)
    739:       compound_clone(:union, dataset, opts)
    740:     end

unlimited()

Returns a copy of the dataset with no limit or offset.

      DB[:items].limit(10, 20).unlimited # SELECT * FROM items

[Source]

         # File lib/sequel/dataset/query.rb, line 745
    745:     def unlimited
    746:       clone(:limit=>nil, :offset=>nil)
    747:     end

unordered()

Returns a copy of the dataset with no order.

      DB[:items].order(:a).unordered # SELECT * FROM items

[Source]

         # File lib/sequel/dataset/query.rb, line 752
    752:     def unordered
    753:       order(nil)
    754:     end

where(*cond, &block)

Add a condition to the WHERE clause. See `filter` for argument types.

      DB[:items].group(:a).having(:a).filter(:b)
      # SELECT * FROM items GROUP BY a HAVING a AND b

      DB[:items].group(:a).having(:a).where(:b)
      # SELECT * FROM items WHERE b GROUP BY a HAVING a

[Source]

         # File lib/sequel/dataset/query.rb, line 763
    763:     def where(*cond, &block)
    764:       _filter(:where, *cond, &block)
    765:     end

with(name, dataset, opts={})

Add a common table expression (CTE) with the given name and a dataset that defines the CTE. A common table expression acts as an inline view for the query. Options:

:args : | Specify the arguments/columns for the CTE, should be an array of symbols.
:recursive : | Specify that this is a recursive CTE

      DB[:items].with(:items, DB[:syx].filter(:name.like('A%')))
      # WITH items AS (SELECT * FROM syx WHERE (name LIKE 'A%')) SELECT * FROM items

[Source]

         # File lib/sequel/dataset/query.rb, line 775
    775:     def with(name, dataset, opts={})
    776:       raise(Error, 'This datatset does not support common table expressions') unless supports_cte?
    777:       clone(:with=>(@opts[:with]||[]) + [opts.merge(:name=>name, :dataset=>dataset)])
    778:     end

with_recursive(name, nonrecursive, recursive, opts={})

Add a recursive common table expression (CTE) with the given name, a dataset that defines the nonrecursive part of the CTE, and a dataset that defines the recursive part of the CTE. Options:

:args : | Specify the arguments/columns for the CTE, should be an array of symbols.
:union_all : | Set to false to use UNION instead of UNION ALL combining the nonrecursive and recursive parts.

      DB[:t].select(:i___id, :pi___parent_id).
       with_recursive(:t,
                      DB[:i1].filter(:parent_id=>nil),
                      DB[:t].join(:t, :i=>:parent_id).select(:i1__id, :i1__parent_id),
                      :args=>[:i, :pi])
      # WITH RECURSIVE t(i, pi) AS (
      #   SELECT * FROM i1 WHERE (parent_id IS NULL)
      #   UNION ALL
      #   SELECT i1.id, i1.parent_id FROM t INNER JOIN t ON (t.i = t.parent_id)
      # )
      # SELECT i AS id, pi AS parent_id FROM t

[Source]

         # File lib/sequel/dataset/query.rb, line 797
    797:     def with_recursive(name, nonrecursive, recursive, opts={})
    798:       raise(Error, 'This datatset does not support common table expressions') unless supports_cte?
    799:       clone(:with=>(@opts[:with]||[]) + [opts.merge(:recursive=>true, :name=>name, :dataset=>nonrecursive.union(recursive, {:all=>opts[:union_all] != false, :from_self=>false}))])
    800:     end

with_sql(sql, *args)

Returns a copy of the dataset with the static SQL used. This is useful if you want to keep the same row_proc/graph, but change the SQL used to custom SQL.

      DB[:items].with_sql('SELECT * FROM foo') # SELECT * FROM foo

[Source]

         # File lib/sequel/dataset/query.rb, line 806
    806:     def with_sql(sql, *args)
    807:       sql = SQL::PlaceholderLiteralString.new(sql, args) unless args.empty?
    808:       clone(:sql=>sql)
    809:     end

### Protected Instance methods

options_overlap(opts)

Return true if the dataset has a non-nil value for any key in opts.

[Source]

         # File lib/sequel/dataset/query.rb, line 814
    814:     def options_overlap(opts)
    815:       !(@opts.collect{|k,v| k unless v.nil?}.compact & opts).empty?
    816:     end

simple_select_all?()

Whether this dataset is a simple SELECT * FROM table.

[Source]

         # File lib/sequel/dataset/query.rb, line 819
    819:     def simple_select_all?
    820:       o = @opts.reject{|k,v| v.nil? || NON_SQL_OPTIONS.include?(k)}
    821:       o.length == 1 && (f = o[:from]) && f.length == 1 && (f.first.is_a?(Symbol) || f.first.is_a?(SQL::AliasedExpression))
    822:     end

## User Methods relating to SQL Creation

These are methods you can call to see what SQL will be generated by the dataset.

### Public Instance methods

delete_sql()

Returns a DELETE SQL query string. See `delete`.

      dataset.filter{|o| o.price >= 100}.delete_sql
      # => "DELETE FROM items WHERE (price >= 100)"

[Source]

        # File lib/sequel/dataset/sql.rb, line 12
    12:     def delete_sql
    13:       return static_sql(opts[:sql]) if opts[:sql]
    14:       check_modification_allowed!
    15:       clause_sql(:delete)
    16:     end

exists()

Returns an EXISTS clause for the dataset as a `LiteralString`.

      DB.select(1).where(DB[:items].exists)
      # SELECT 1 WHERE (EXISTS (SELECT * FROM items))

[Source]

        # File lib/sequel/dataset/sql.rb, line 22
    22:     def exists
    23:       LiteralString.new("EXISTS (#{select_sql})")
    24:     end

insert_sql(*values)

Returns an INSERT SQL query string. See `insert`.

      DB[:items].insert_sql(:a=>1)
      # => "INSERT INTO items (a) VALUES (1)"

[Source]

        # File lib/sequel/dataset/sql.rb, line 30
    30:     def insert_sql(*values)
    31:       return static_sql(@opts[:sql]) if @opts[:sql]
    32:
    33:       check_modification_allowed!
    34:
    35:       columns = []
    36:
    37:       case values.size
    38:       when 0
    39:         return insert_sql({})
    40:       when 1
    41:         case vals = values.at(0)
    42:         when Hash
    43:           vals = @opts[:defaults].merge(vals) if @opts[:defaults]
    44:           vals = vals.merge(@opts[:overrides]) if @opts[:overrides]
    45:           values = []
    46:           vals.each do |k,v|
    47:             columns << k
    48:             values << v
    49:           end
    50:         when Dataset, Array, LiteralString
    51:           values = vals
    52:         else
    53:           if vals.respond_to?(:values) && (v = vals.values).is_a?(Hash)
    54:             return insert_sql(v)
    55:           end
    56:         end
    57:       when 2
    58:         if (v0 = values.at(0)).is_a?(Array) && ((v1 = values.at(1)).is_a?(Array) || v1.is_a?(Dataset) || v1.is_a?(LiteralString))
    59:           columns, values = v0, v1
    60:           raise(Error, "Different number of values and columns given to insert_sql") if values.is_a?(Array) and columns.length != values.length
    61:         end
    62:       end
    63:
    64:       columns = columns.map{|k| literal(String === k ? k.to_sym : k)}
    65:       clone(:columns=>columns, :values=>values)._insert_sql
    66:     end

literal(v)

Returns a literal representation of a value to be used as part of an SQL expression.

      DB[:items].literal("abc'def\\") #=> "'abc''def\\\\'"
      DB[:items].literal(:items__id) #=> "items.id"
      DB[:items].literal([1, 2, 3]) => "(1, 2, 3)"
      DB[:items].literal(DB[:items]) => "(SELECT * FROM items)"
      DB[:items].literal(:x + 1 > :y) => "((x + 1) > y)"

If an unsupported object is given, an `Error` is raised.

[Source]

         # File lib/sequel/dataset/sql.rb, line 78
     78:     def literal(v)
     79:       case v
     80:       when String
     81:         return v if v.is_a?(LiteralString)
     82:         v.is_a?(SQL::Blob) ? literal_blob(v) : literal_string(v)
     83:       when Symbol
     84:         literal_symbol(v)
     85:       when Integer
     86:         literal_integer(v)
     87:       when Hash
     88:         literal_hash(v)
     89:       when SQL::Expression
     90:         literal_expression(v)
     91:       when Float
     92:         literal_float(v)
     93:       when BigDecimal
     94:         literal_big_decimal(v)
     95:       when NilClass
     96:         literal_nil
     97:       when TrueClass
     98:         literal_true
     99:       when FalseClass
    100:         literal_false
    101:       when Array
    102:         literal_array(v)
    103:       when Time
    104:         literal_time(v)
    105:       when DateTime
    106:         literal_datetime(v)
    107:       when Date
    108:         literal_date(v)
    109:       when Dataset
    110:         literal_dataset(v)
    111:       else
    112:         literal_other(v)
    113:       end
    114:     end

multi_insert_sql(columns, values)

Returns an array of insert statements for inserting multiple records. This method is used by `multi_insert` to format insert statements and expects a keys array and and an array of value arrays.

This method should be overridden by descendants if the support inserting multiple records in a single SQL statement.

[Source]

         # File lib/sequel/dataset/sql.rb, line 122
    122:     def multi_insert_sql(columns, values)
    123:       values.map{|r| insert_sql(columns, r)}
    124:     end

select_sql()

Returns a SELECT SQL query string.

      dataset.select_sql # => "SELECT * FROM items"

[Source]

         # File lib/sequel/dataset/sql.rb, line 129
    129:     def select_sql
    130:       return static_sql(@opts[:sql]) if @opts[:sql]
    131:       clause_sql(:select)
    132:     end

sql()

Same as `select_sql`, not aliased directly to make subclassing simpler.

[Source]

         # File lib/sequel/dataset/sql.rb, line 135
    135:     def sql
    136:       select_sql
    137:     end

truncate_sql()

Returns a TRUNCATE SQL query string. See `truncate`

      DB[:items].truncate_sql # => 'TRUNCATE items'

[Source]

         # File lib/sequel/dataset/sql.rb, line 142
    142:     def truncate_sql
    143:       if opts[:sql]
    144:         static_sql(opts[:sql])
    145:       else
    146:         check_modification_allowed!
    147:         raise(InvalidOperation, "Can't truncate filtered datasets") if opts[:where]
    148:         _truncate_sql(source_list(opts[:from]))
    149:       end
    150:     end

update_sql(values = {})

Formats an UPDATE statement using the given values. See `update`.

      DB[:items].update_sql(:price => 100, :category => 'software')
      # => "UPDATE items SET price = 100, category = 'software'

Raises an `Error` if the dataset is grouped or includes more than one table.

[Source]

         # File lib/sequel/dataset/sql.rb, line 159
    159:     def update_sql(values = {})
    160:       return static_sql(opts[:sql]) if opts[:sql]
    161:       check_modification_allowed!
    162:       clone(:values=>values)._update_sql
    163:     end

## Internal Methods relating to SQL Creation

These methods, while public, are not designed to be used directly by the end user.

### Constants

AND_SEPARATOR | = | " AND ".freeze
BOOL_FALSE | = | "'f'".freeze
BOOL_TRUE | = | "'t'".freeze
COMMA_SEPARATOR | = | ', '.freeze
COLUMN_REF_RE1 | = | /\A([\w ]+)__([\w ]+)___([\w ]+)\z/.freeze
COLUMN_REF_RE2 | = | /\A([\w ]+)___([\w ]+)\z/.freeze
COLUMN_REF_RE3 | = | /\A([\w ]+)__([\w ]+)\z/.freeze
COUNT_FROM_SELF_OPTS | = | [:distinct, :group, :sql, :limit, :compounds]
COUNT_OF_ALL_AS_COUNT | = | SQL::Function.new(:count, LiteralString.new('*'.freeze)).as(:count)
DATASET_ALIAS_BASE_NAME | = | 't'.freeze
FOR_UPDATE | = | ' FOR UPDATE'.freeze
IS_LITERALS | = | {nil=>'NULL'.freeze, true=>'TRUE'.freeze, false=>'FALSE'.freeze}.freeze
IS_OPERATORS | = | ::Sequel::SQL::ComplexExpression::IS_OPERATORS
N_ARITY_OPERATORS | = | ::Sequel::SQL::ComplexExpression::N_ARITY_OPERATORS
NULL | = | "NULL".freeze
QUALIFY_KEYS | = | [:select, :where, :having, :order, :group]
QUESTION_MARK | = | '?'.freeze
DELETE_CLAUSE_METHODS | = | clause_methods(:delete, %w'from where')
INSERT_CLAUSE_METHODS | = | clause_methods(:insert, %w'into columns values')
SELECT_CLAUSE_METHODS | = | clause_methods(:select, %w'with distinct columns from join where group having compounds order limit lock')
UPDATE_CLAUSE_METHODS | = | clause_methods(:update, %w'table set where')
TIMESTAMP_FORMAT | = | "'%Y-%m-%d %H:%M:%S%N%z'".freeze
STANDARD_TIMESTAMP_FORMAT | = | "TIMESTAMP #{TIMESTAMP_FORMAT}".freeze
TWO_ARITY_OPERATORS | = | ::Sequel::SQL::ComplexExpression::TWO_ARITY_OPERATORS
WILDCARD | = | LiteralString.new('*').freeze
SQL_WITH | = | "WITH ".freeze

### Public Class methods

clause_methods(type, clauses)

Given a type (e.g. select) and an array of clauses, return an array of methods to call to build the SQL string.

[Source]

         # File lib/sequel/dataset/sql.rb, line 172
    172:     def self.clause_methods(type, clauses)
    173:       clauses.map{|clause| "#{type}_#{clause}_sql""#{type}_#{clause}_sql"}.freeze
    174:     end

### Public Instance methods

aliased_expression_sql(ae)

SQL fragment for AliasedExpression

[Source]

         # File lib/sequel/dataset/sql.rb, line 204
    204:     def aliased_expression_sql(ae)
    205:       as_sql(literal(ae.expression), ae.aliaz)
    206:     end

array_sql(a)

SQL fragment for Array

[Source]

         # File lib/sequel/dataset/sql.rb, line 209
    209:     def array_sql(a)
    210:       a.empty? ? '(NULL)' : "(#{expression_list(a)})"
    211:     end

boolean_constant_sql(constant)

SQL fragment for BooleanConstants

[Source]

         # File lib/sequel/dataset/sql.rb, line 214
    214:     def boolean_constant_sql(constant)
    215:       literal(constant)
    216:     end

case_expression_sql(ce)

SQL fragment for CaseExpression

[Source]

         # File lib/sequel/dataset/sql.rb, line 219
    219:     def case_expression_sql(ce)
    220:       sql = '(CASE '
    221:       sql << "#{literal(ce.expression)} " if ce.expression?
    222:       ce.conditions.collect{ |c,r|
    223:         sql << "WHEN #{literal(c)} THEN #{literal(r)} "
    224:       }
    225:       sql << "ELSE #{literal(ce.default)} END)"
    226:     end

cast_sql(expr, type)

SQL fragment for the SQL CAST expression

[Source]

         # File lib/sequel/dataset/sql.rb, line 229
    229:     def cast_sql(expr, type)
    230:       "CAST(#{literal(expr)} AS #{db.cast_type_literal(type)})"
    231:     end

column_all_sql(ca)

SQL fragment for specifying all columns in a given table

[Source]

         # File lib/sequel/dataset/sql.rb, line 234
    234:     def column_all_sql(ca)
    235:       "#{quote_schema_table(ca.table)}.*"
    236:     end

complex_expression_sql(op, args)

SQL fragment for complex expressions

[Source]

         # File lib/sequel/dataset/sql.rb, line 239
    239:     def complex_expression_sql(op, args)
    240:       case op
    241:       when *IS_OPERATORS
    242:         r = args.at(1)
    243:         if r.nil? || supports_is_true?
    244:           raise(InvalidOperation, 'Invalid argument used for IS operator') unless v = IS_LITERALS[r]
    245:           "(#{literal(args.at(0))} #{op} #{v})"
    246:         elsif op == :IS
    247:           complex_expression_sql("=""=", args)
    248:         else
    249:           complex_expression_sql(:OR, [SQL::BooleanExpression.new("!=""!=", *args), SQL::BooleanExpression.new(:IS, args.at(0), nil)])
    250:         end
    251:       when :IN, "NOT IN""NOT IN"
    252:         cols = args.at(0)
    253:         vals = args.at(1)
    254:         col_array = true if cols.is_a?(Array)
    255:         if vals.is_a?(Array)
    256:           val_array = true
    257:           empty_val_array = vals == []
    258:         end
    259:         if col_array
    260:           if empty_val_array
    261:             if op == :IN
    262:               literal(SQL::BooleanExpression.from_value_pairs(cols.to_a.map{|x| [x, x]}, :AND, true))
    263:             else
    264:               literal(1=>1)
    265:             end
    266:           elsif !supports_multiple_column_in?
    267:             if val_array
    268:               expr = SQL::BooleanExpression.new(:OR, *vals.to_a.map{|vs| SQL::BooleanExpression.from_value_pairs(cols.to_a.zip(vs).map{|c, v| [c, v]})})
    269:               literal(op == :IN ? expr : ~expr)
    270:             else
    271:               old_vals = vals
    272:               vals = vals.to_a
    273:               val_cols = old_vals.columns
    274:               complex_expression_sql(op, [cols, vals.map!{|x| x.values_at(*val_cols)}])
    275:             end
    276:           else
    277:             # If the columns and values are both arrays, use array_sql instead of
    278:             # literal so that if values is an array of two element arrays, it
    279:             # will be treated as a value list instead of a condition specifier.
    280:             "(#{literal(cols)} #{op} #{val_array ? array_sql(vals) : literal(vals)})"
    281:           end
    282:         else
    283:           if empty_val_array
    284:             if op == :IN
    285:               literal(SQL::BooleanExpression.from_value_pairs([[cols, cols]], :AND, true))
    286:             else
    287:               literal(1=>1)
    288:             end
    289:           else
    290:             "(#{literal(cols)} #{op} #{literal(vals)})"
    291:           end
    292:         end
    293:       when *TWO_ARITY_OPERATORS
    294:         "(#{literal(args.at(0))} #{op} #{literal(args.at(1))})"
    295:       when *N_ARITY_OPERATORS
    296:         "(#{args.collect{|a| literal(a)}.join(" #{op} ")})"
    297:       when :NOT
    298:         "NOT #{literal(args.at(0))}"
    299:       when :NOOP
    300:         literal(args.at(0))
    301:       when 'B~''B~'
    302:         "~#{literal(args.at(0))}"
    303:       else
    304:         raise(InvalidOperation, "invalid operator #{op}")
    305:       end
    306:     end

constant_sql(constant)

SQL fragment for constants

[Source]

         # File lib/sequel/dataset/sql.rb, line 309
    309:     def constant_sql(constant)
    310:       constant.to_s
    311:     end

function_sql(f)

SQL fragment specifying an SQL function call

[Source]

         # File lib/sequel/dataset/sql.rb, line 314
    314:     def function_sql(f)
    315:       args = f.args
    316:       "#{f.f}#{args.empty? ? '()' : literal(args)}"
    317:     end

join_clause_sql(jc)

SQL fragment specifying a JOIN clause without ON or USING.

[Source]

         # File lib/sequel/dataset/sql.rb, line 320
    320:     def join_clause_sql(jc)
    321:       table = jc.table
    322:       table_alias = jc.table_alias
    323:       table_alias = nil if table == table_alias
    324:       tref = table_ref(table)
    325:       " #{join_type_sql(jc.join_type)} #{table_alias ? as_sql(tref, table_alias) : tref}"
    326:     end

join_on_clause_sql(jc)

SQL fragment specifying a JOIN clause with ON.

[Source]

         # File lib/sequel/dataset/sql.rb, line 329
    329:     def join_on_clause_sql(jc)
    330:       "#{join_clause_sql(jc)} ON #{literal(filter_expr(jc.on))}"
    331:     end

join_using_clause_sql(jc)

SQL fragment specifying a JOIN clause with USING.

[Source]

         # File lib/sequel/dataset/sql.rb, line 334
    334:     def join_using_clause_sql(jc)
    335:       "#{join_clause_sql(jc)} USING (#{column_list(jc.using)})"
    336:     end

negative_boolean_constant_sql(constant)

SQL fragment for NegativeBooleanConstants

[Source]

         # File lib/sequel/dataset/sql.rb, line 339
    339:     def negative_boolean_constant_sql(constant)
    340:       "NOT #{boolean_constant_sql(constant)}"
    341:     end

ordered_expression_sql(oe)

SQL fragment for the ordered expression, used in the ORDER BY clause.

[Source]

         # File lib/sequel/dataset/sql.rb, line 345
    345:     def ordered_expression_sql(oe)
    346:       s = "#{literal(oe.expression)} #{oe.descending ? 'DESC' : 'ASC'}"
    347:       case oe.nulls
    348:       when :first
    349:         "#{s} NULLS FIRST"
    350:       when :last
    351:         "#{s} NULLS LAST"
    352:       else
    353:         s
    354:       end
    355:     end

placeholder_literal_string_sql(pls)

SQL fragment for a literal string with placeholders

[Source]

         # File lib/sequel/dataset/sql.rb, line 358
    358:     def placeholder_literal_string_sql(pls)
    359:       args = pls.args
    360:       s = if args.is_a?(Hash)
    361:         re = /:(#{args.keys.map{|k| Regexp.escape(k.to_s)}.join('|')})\b/
    362:         pls.str.gsub(re){literal(args[$1.to_sym])}
    363:       else
    364:         i = -1
    365:         pls.str.gsub(QUESTION_MARK){literal(args.at(i+=1))}
    366:       end
    367:       s = "(#{s})" if pls.parens
    368:       s
    369:     end

qualified_identifier_sql(qcr)

SQL fragment for the qualifed identifier, specifying a table and a column (or schema and table).

[Source]

         # File lib/sequel/dataset/sql.rb, line 373
    373:     def qualified_identifier_sql(qcr)
    374:       [qcr.table, qcr.column].map{|x| [SQL::QualifiedIdentifier, SQL::Identifier, Symbol].any?{|c| x.is_a?(c)} ? literal(x) : quote_identifier(x)}.join('.')
    375:     end

quote_identifier(name)

Adds quoting to identifiers (columns and tables). If identifiers are not being quoted, returns name as a string. If identifiers are being quoted quote the name with quoted_identifier.

[Source]

         # File lib/sequel/dataset/sql.rb, line 380
    380:     def quote_identifier(name)
    381:       return name if name.is_a?(LiteralString)
    382:       name = name.value if name.is_a?(SQL::Identifier)
    383:       name = input_identifier(name)
    384:       name = quoted_identifier(name) if quote_identifiers?
    385:       name
    386:     end

quote_schema_table(table)

Separates the schema from the table and returns a string with them quoted (if quoting identifiers)

[Source]

         # File lib/sequel/dataset/sql.rb, line 390
    390:     def quote_schema_table(table)
    391:       schema, table = schema_and_table(table)
    392:       "#{"#{quote_identifier(schema)}." if schema}#{quote_identifier(table)}"
    393:     end

quoted_identifier(name)

This method quotes the given name with the SQL standard double quote. should be overridden by subclasses to provide quoting not matching the SQL standard, such as backtick (used by MySQL and SQLite).

[Source]

         # File lib/sequel/dataset/sql.rb, line 398
    398:     def quoted_identifier(name)
    399:       "\"#{name.to_s.gsub('"', '""')}\""
    400:     end

schema_and_table(table_name)

Split the schema information from the table

[Source]

         # File lib/sequel/dataset/sql.rb, line 403
    403:     def schema_and_table(table_name)
    404:       sch = db.default_schema if db
    405:       case table_name
    406:       when Symbol
    407:         s, t, a = split_symbol(table_name)
    408:         [s||sch, t]
    409:       when SQL::QualifiedIdentifier
    410:         [table_name.table, table_name.column]
    411:       when SQL::Identifier
    412:         [sch, table_name.value]
    413:       when String
    414:         [sch, table_name]
    415:       else
    416:         raise Error, 'table_name should be a Symbol, SQL::QualifiedIdentifier, SQL::Identifier, or String'
    417:       end
    418:     end

subscript_sql(s)

SQL fragment for specifying subscripts (SQL array accesses)

[Source]

         # File lib/sequel/dataset/sql.rb, line 421
    421:     def subscript_sql(s)
    422:       "#{literal(s.f)}[#{expression_list(s.sub)}]"
    423:     end

window_function_sql(function, window)

The SQL fragment for the given window function‘s function and window.

[Source]

         # File lib/sequel/dataset/sql.rb, line 447
    447:     def window_function_sql(function, window)
    448:       "#{literal(function)} OVER #{literal(window)}"
    449:     end

window_sql(opts)

The SQL fragment for the given window‘s options.

[Source]

         # File lib/sequel/dataset/sql.rb, line 426
    426:     def window_sql(opts)
    427:       raise(Error, 'This dataset does not support window functions') unless supports_window_functions?
    428:       window = literal(opts[:window]) if opts[:window]
    429:       partition = "PARTITION BY #{expression_list(Array(opts[:partition]))}" if opts[:partition]
    430:       order = "ORDER BY #{expression_list(Array(opts[:order]))}" if opts[:order]
    431:       frame = case opts[:frame]
    432:         when nil
    433:           nil
    434:         when :all
    435:           "ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING"
    436:         when :rows
    437:           "ROWS UNBOUNDED PRECEDING"
    438:         when String
    439:           opts[:frame]
    440:         else
    441:           raise Error, "invalid window frame clause, should be :all, :rows, a string, or nil"
    442:       end
    443:       "(#{[window, partition, order, frame].compact.join(' ')})"
    444:     end

### Protected Instance methods

_insert_sql()

Formats in INSERT statement using the stored columns and values.

[Source]

         # File lib/sequel/dataset/sql.rb, line 454
    454:     def _insert_sql
    455:       clause_sql(:insert)
    456:     end

_update_sql()

Formats an UPDATE statement using the stored values.

[Source]

         # File lib/sequel/dataset/sql.rb, line 459
    459:     def _update_sql
    460:       clause_sql(:update)
    461:     end

compound_from_self()

Return a from_self dataset if an order or limit is specified, so it works as expected with UNION, EXCEPT, and INTERSECT clauses.

[Source]

         # File lib/sequel/dataset/sql.rb, line 465
    465:     def compound_from_self
    466:       (@opts[:limit] || @opts[:order]) ? from_self : self
    467:     end

## Mutation methods

These methods modify the receiving dataset and should be used with care.

### Classes and Modules

Module Sequel::Dataset::Pagination
Module Sequel::Dataset::QueryBlockCopy

### Constants

MUTATION_METHODS | = | QUERY_METHODS |  | All methods that should have a ! method added that modifies the receiver.
TO_DOT_OPTIONS | = | [:with, :distinct, :select, :from, :join, :where, :group, :having, :compounds, :order, :limit, :offset, :lock].freeze |  | The option keys that should be included in the dot output.

### Attributes

identifier_input_method | [RW] | Set the method to call on identifiers going into the database for this dataset
identifier_output_method | [RW] | Set the method to call on identifiers coming the database for this dataset
quote_identifiers | [W] | Whether to quote identifiers for this dataset
row_proc | [RW] | The row_proc for this database, should be a Proc that takes a single hash argument and returns the object you want each to return.

### Public Class methods

def_mutation_method(*meths)

Setup mutation (e.g. filter!) methods. These operate the same as the non-! methods, but replace the options of the current dataset with the options of the resulting dataset.

[Source]

        # File lib/sequel/dataset/mutation.rb, line 14
    14:     def self.def_mutation_method(*meths)
    15:       meths.each do |meth|
    16:         class_eval("def #{meth}!(*args, &block); mutation_method(:#{meth}, *args, &block) end", __FILE__, __LINE__)
    17:       end
    18:     end

### Public Instance methods

def_mutation_method(*meths)

Add a mutation method to this dataset instance.

[Source]

        # File lib/sequel/dataset/mutation.rb, line 38
    38:     def def_mutation_method(*meths)
    39:       meths.each do |meth|
    40:         instance_eval("def #{meth}!(*args, &block); mutation_method(:#{meth}, *args, &block) end", __FILE__, __LINE__)
    41:       end
    42:     end

each_page(page_size) {|paginate(page_no, page_size, record_count)}| ...}

Yields a paginated dataset for each page and returns the receiver. Does a count to find the total number of records for this dataset.

[Source]

        # File lib/sequel/extensions/pagination.rb, line 20
    20:     def each_page(page_size)
    21:       raise(Error, "You cannot paginate a dataset that already has a limit") if @opts[:limit]
    22:       record_count = count
    23:       total_pages = (record_count / page_size.to_f).ceil
    24:       (1..total_pages).each{|page_no| yield paginate(page_no, page_size, record_count)}
    25:       self
    26:     end

paginate(page_no, page_size, record_count=nil)

Returns a paginated dataset. The returned dataset is limited to the page size at the correct offset, and extended with the Pagination module. If a record count is not provided, does a count of total number of records for this dataset.

[Source]

        # File lib/sequel/extensions/pagination.rb, line 11
    11:     def paginate(page_no, page_size, record_count=nil)
    12:       raise(Error, "You cannot paginate a dataset that already has a limit") if @opts[:limit]
    13:       paginated = limit(page_size, (page_no - 1) * page_size)
    14:       paginated.extend(Pagination)
    15:       paginated.set_pagination_info(page_no, page_size, record_count || count)
    16:     end

print(*cols)

Pretty prints the records in the dataset as plain-text table.

[Source]

        # File lib/sequel/extensions/pretty_table.rb, line 8
     8:     def print(*cols)
     9:       Sequel::PrettyTable.print(naked.all, cols.empty? ? columns : cols)
    10:     end

query(&block)

Translates a query block into a dataset. Query blocks can be useful when expressing complex SELECT statements, e.g.:

      dataset = DB[:items].query do
        select :x, :y, :z
        filter{|o| (o.x > 1) & (o.y > 2)}
        order :z.desc
      end

Which is the same as:

     dataset = DB[:items].select(:x, :y, :z).filter{|o| (o.x > 1) & (o.y > 2)}.order(:z.desc)

Note that inside a call to query, you cannot call each, insert, update, or delete (or any method that calls those), or Sequel will raise an error.

[Source]

        # File lib/sequel/extensions/query.rb, line 30
    30:     def query(&block)
    31:       copy = clone({})
    32:       copy.extend(QueryBlockCopy)
    33:       copy.instance_eval(&block)
    34:       clone(copy.opts)
    35:     end

to_dot()

Return a string that can be processed by the `dot` program (included with graphviz) in order to see a visualization of the dataset‘s abstract syntax tree.

[Source]

        # File lib/sequel/extensions/to_dot.rb, line 14
    14:     def to_dot
    15:       i = 0
    16:       dot = ["digraph G {", "#{i} [label=\"self\"];"]
    17:       _to_dot(dot, "", i, self, i)
    18:       dot << "}"
    19:       dot.join("\n")
    20:     end

[Validate]