Module | ActiveRecord::ConnectionAdapters::SchemaStatements
In: | lib/active_record/connection_adapters/abstract/schema_statements.rb

### Methods

add_column add_index add_order_by_for_association_limiting! add_timestamps assume_migrated_upto_version change_column change_column_default change_table columns create_table distinct drop_table index_exists? initialize_schema_migrations_table native_database_types options_include_default? quoted_columns_for_index remove_column remove_columns remove_index remove_timestamps rename_column rename_index rename_table structure_dump table_alias_for table_exists?

### Public Instance methods

add_column(table_name, column_name, type, options = {})

Adds a new column to the named table. See TableDefinition#column for details of the options you can use.

add_index(table_name, column_name, options = {})

Adds a new index to the table. `column_name` can be a single Symbol, or an Array of Symbols.

The index will be named after the table and the first column name, unless you pass `:name` as an option.

When creating an index on multiple columns, the first column is used as a name for the index. For example, when you specify an index on two columns [`:first`, `:last`], the DBMS creates an index for both columns as well as an index for the first column `:first`. Using just the first name for this index makes sense, because you will never have to create a singular index with this name.

##### Examples

###### Creating a simple index

     add_index(:suppliers, :name)

generates

     CREATE INDEX suppliers_name_index ON suppliers(name)

###### Creating a unique index

     add_index(:accounts, [:branch_id, :party_id], :unique => true)

generates

     CREATE UNIQUE INDEX accounts_branch_id_party_id_index ON accounts(branch_id, party_id)

###### Creating a named index

     add_index(:accounts, [:branch_id, :party_id], :unique => true, :name => 'by_branch_party')

generates

     CREATE UNIQUE INDEX by_branch_party ON accounts(branch_id, party_id)

###### Creating an index with specific key length

     add_index(:accounts, :name, :name => 'by_name', :length => 10)

generates

     CREATE INDEX by_name ON accounts(name(10))

     add_index(:accounts, [:name, :surname], :name => 'by_name_surname', :length => {:name => 10, :surname => 15})

generates

     CREATE INDEX by_name_surname ON accounts(name(10), surname(15))

Note: SQLite doesn‘t support index length

add_order_by_for_association_limiting!(sql, options)

ORDER BY clause for the passed order option. PostgreSQL overrides this due to its stricter standards compliance.

add_timestamps(table_name)

Adds timestamps (created_at and updated_at) columns to the named table.

##### Examples

     add_timestamps(:suppliers)

assume_migrated_upto_version(version, migrations_path = ActiveRecord::Migrator.migrations_path)
change_column(table_name, column_name, type, options = {})

Changes the column‘s definition according to the new options. See TableDefinition#column for details of the options you can use.

##### Examples

     change_column(:suppliers, :name, :string, :limit => 80)
     change_column(:accounts, :description, :text)

change_column_default(table_name, column_name, default)

Sets a new default value for a column. If you want to set the default value to `NULL`, you are out of luck. You need to DatabaseStatements#execute the appropriate SQL statement yourself.

##### Examples

     change_column_default(:suppliers, :qualification, 'new')
     change_column_default(:accounts, :authorized, 1)

change_table(table_name) {|Table.new(table_name, self)| ...}

A block for changing columns in `table`.

### Example

     # change_table() yields a Table instance
     change_table(:suppliers) do |t|
       t.column :name, :string, :limit => 60
       # Other column alterations here
     end

##### Examples

###### Add a column

     change_table(:suppliers) do |t|
       t.column :name, :string, :limit => 60
     end

###### Add 2 integer columns

     change_table(:suppliers) do |t|
       t.integer :width, :height, :null => false, :default => 0
     end

###### Add created_at/updated_at columns

     change_table(:suppliers) do |t|
       t.timestamps
     end

###### Add a foreign key column

     change_table(:suppliers) do |t|
       t.references :company
     end

Creates a `company_id(integer)` column

###### Add a polymorphic foreign key column

     change_table(:suppliers) do |t|
       t.belongs_to :company, :polymorphic => true
     end

Creates `company_type(varchar)` and `company_id(integer)` columns

###### Remove a column

     change_table(:suppliers) do |t|
       t.remove :company
     end

###### Remove several columns

     change_table(:suppliers) do |t|
       t.remove :company_id
       t.remove :width, :height
     end

###### Remove an index

     change_table(:suppliers) do |t|
       t.remove_index :company_id
     end

See also Table for details on all of the various column transformation

columns(table_name, name = nil)

Returns an array of Column objects for the table specified by `table_name`. See the concrete implementation for details on the expected parameter values.

create_table(table_name, options = {}) {|table_definition if block_given?| ...}

Creates a new table with the name `table_name`. `table_name` may either be a String or a Symbol.

There are two ways to work with `create_table`. You can use the block form or the regular form, like this:

### Block form

     # create_table() passes a TableDefinition object to the block.
     # This form will not only create the table, but also columns for the
     # table.
     create_table(:suppliers) do |t|
       t.column :name, :string, :limit => 60
       # Other fields here
     end

### Regular form

     # Creates a table called 'suppliers' with no columns.
     create_table(:suppliers)
     # Add a column to 'suppliers'.
     add_column(:suppliers, :name, :string, {:limit => 60})

The `options` hash can include the following keys:

`:id`
  Whether to automatically add a primary key column. Defaults to true. Join tables for `has_and_belongs_to_many` should set `:id => false`.
`:primary_key`
  The name of the primary key, if one is to be added automatically. Defaults to `id`.
`:options`
  Any extra options you want appended to the table definition.
`:temporary`
  Make a temporary table.
`:force`
  Set to true to drop the table before creating it. Defaults to false.

##### Examples

###### Add a backend specific option to the generated SQL (MySQL)

     create_table(:suppliers, :options => 'ENGINE=InnoDB DEFAULT CHARSET=utf8')

generates:

     CREATE TABLE suppliers (
       id int(11) DEFAULT NULL auto_increment PRIMARY KEY
     ) ENGINE=InnoDB DEFAULT CHARSET=utf8

###### Rename the primary key column

     create_table(:objects, :primary_key => 'guid') do |t|
       t.column :name, :string, :limit => 80
     end

generates:

     CREATE TABLE objects (
       guid int(11) DEFAULT NULL auto_increment PRIMARY KEY,
       name varchar(80)
     )

###### Do not add a primary key column

     create_table(:categories_suppliers, :id => false) do |t|
       t.column :category_id, :integer
       t.column :supplier_id, :integer
     end

generates:

     CREATE TABLE categories_suppliers (
       category_id int,
       supplier_id int
     )

See also TableDefinition#column for details on how to create columns.

distinct(columns, order_by)

SELECT DISTINCT clause for a given set of columns and a given ORDER BY clause. Both PostgreSQL and Oracle overrides this for custom DISTINCT syntax.

      distinct("posts.id", "posts.created_at desc")

drop_table(table_name, options = {})

Drops a table from the database.

index_exists?(table_name, index_name, default)

Verify the existence of an index.

The default argument is returned if the underlying implementation does not define the indexes method, as there‘s no way to determine the correct answer in that case.

initialize_schema_migrations_table()

Should not be called normally, but this operation is non-destructive. The migrations module handles this automatically.

native_database_types()

Returns a Hash of mappings from the abstract data types to the native database types. See TableDefinition#column for details on the recognized abstract data types.

remove_column(table_name, *column_names)

Removes the column(s) from the table definition.

##### Examples

     remove_column(:suppliers, :qualification)
     remove_columns(:suppliers, :qualification, :experience)

remove_columns(table_name, *column_names)

Alias for remove_column

remove_index(table_name, options = {})

Remove the given index from the table.

Remove the suppliers_name_index in the suppliers table.

      remove_index :suppliers, :name

Remove the index named accounts_branch_id_index in the accounts table.

      remove_index :accounts, :column => :branch_id

Remove the index named accounts_branch_id_party_id_index in the accounts table.

      remove_index :accounts, :column => [:branch_id, :party_id]

Remove the index named by_branch_party in the accounts table.

      remove_index :accounts, :name => :by_branch_party

remove_timestamps(table_name)

Removes the timestamp columns (created_at and updated_at) from the table definition.

##### Examples

     remove_timestamps(:suppliers)

rename_column(table_name, column_name, new_column_name)

Renames a column.

##### Example

     rename_column(:suppliers, :description, :name)

rename_index(table_name, old_name, new_name)

Rename an index.

Rename the index_people_on_last_name index to index_users_on_last_name

      rename_index :people, 'index_people_on_last_name', 'index_users_on_last_name'

rename_table(table_name, new_name)

Renames a table.

##### Example

     rename_table('octopuses', 'octopi')

structure_dump()

Returns a string of `CREATE TABLE` SQL statement(s) for recreating the entire structure of the database.

table_alias_for(table_name)

Truncates a table alias according to the limits of the current adapter.

table_exists?(table_name)

def tables(name = nil) end

### Protected Instance methods

options_include_default?(options)
quoted_columns_for_index(column_names, options = {})

Overridden by the mysql adapter for supporting index lengths

[Validate]