▼ |  | DB: Database Connectivity

1 | Using Database Connections
2 | Connections
3 | Queries
4 | SQL Types and Conversions
5 | Utilities
6 | Notes

► | 4 | SQL Types and Conversions

4.1 | SQL Type Conversions
4.2 | SQL Data

On this page:

4.1`` SQL Type Conversions
4.1.1`` Postgre SQL Types
4.1.2`` My SQL Types
4.1.3`` SQLite Types
4.1.4`` ODBC Types
4.2`` SQL Data
4.2.1`` SQL NULL
sql-null
sql-null?
sql-null->false
false->sql-null
4.2.2`` Dates and Times
sql-date
sql-time
sql-timestamp
sql-interval
sql-year-month-interval?
sql-day-time-interval?
sql-interval->sql-time
sql-time->sql-interval
4.2.3`` Bits
make-sql-bits
sql-bits?
sql-bits-length
sql-bits-ref
sql-bits-set!
sql-bits->list
sql-bits->string
list->sql-bits
string->sql-bits

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### 4`` SQL Types and Conversions

Connections automatically convert query results to appropriate Racket types. Likewise, query parameters are accepted as Racket values and converted to the appropriate SQL type.

Examples:

> > (query-value pgc "select count(*) from the_numbers")
> 4
> > (query-value pgc "select false")
> #f
> > (query-value pgc "select 1 + $1" 2)
> 3

If a query result contains a column with a SQL type not supported by this library, an exception is raised. As a workaround, cast the column to a supported type:

Examples:

> > (query-value pgc "select inet '127.0.0.1'")
> query-value: unsupported type: inet (typeid 869)
> > (query-value pgc "select cast(inet '127.0.0.1' as varchar)")
> "127.0.0.1/32"

The exception for unsupported types in result columns is raised when the query is executed, not when it is prepared; for parameters it is raised when the parameter values are supplied. Thus even unexecutable prepared statements can be inspected using prepared-statement-parameter-types and prepared-statement-result-types.

#### 4.1`` SQL Type Conversions

This section describes the correspondences between SQL types and Racket types for the supported database systems.

##### 4.1.1`` PostgreSQL Types

This section applies to connections created with postgresql-connect.

The following table lists the PostgreSQL types known to this library, along with their corresponding Racket representations.

> PostgreSQL type |  | pg_type.typname |  | Racket type
> 'boolean |  | bool |  | boolean?
> 'char1 |  | char |  | char?
> 'smallint |  | int2 |  | exact-integer?
> 'integer |  | int4 |  | exact-integer?
> 'bigint |  | int8 |  | exact-integer?
> 'real |  | float4 |  | real?
> 'double |  | float8 |  | real?
> 'decimal |  | numeric |  | number?
> 'character |  | bpchar |  | string?
> 'varchar |  | varchar |  | string?
> 'text |  | text |  | string?
> 'bytea |  | bytea |  | bytes?
> 'date |  | date |  | sql-date?
> 'time |  | time |  | sql-time?
> 'timetz |  | timetz |  | sql-time?
> 'timestamp |  | timestamp |  | sql-timestamp?
> 'timestamptz |  | timestamptz |  | sql-timestamp?
> 'interval |  | interval |  | sql-interval?
> 'bit |  | bit |  | sql-bits?
> 'varbit |  | varbit |  | sql-bits?
> 'point |  | point |  | point?
> 'lseg |  | lseg |  | line?
> 'path |  | path |  | pg-path?
> 'box |  | box |  | pg-box?
> 'polygon |  | polygon |  | polygon?
> 'circle |  | circle |  | pg-circle?

The 'char1 type, written "char" in PostgreSQL’s SQL syntax (the quotation marks are significant), is one byte, essentially a tiny integer written as a character.

A SQL value of type decimal is converted to either an exact rational or +nan.0. When converting Racket values to SQL decimal, exact rational values representable by finite decimal strings are converted without loss of precision. (Precision may be lost, of course, if the value is then stored in a database field of lower precision.) Other real values are converted to decimals with a loss of precision. In PostgreSQL, numeric and decimal refer to the same type.

Examples:

> > (query-value pgc "select real '+Infinity'")
> +inf.0
> > (query-value pgc "select numeric '12345678901234567890'")
> 12345678901234567890

The geometric types such as 'point are represented by structures defined in the db/util/geometry and db/util/postgresql modules.

PostgreSQL user-defined domains are supported in query results if the underlying type is supported. Recordset headers and prepared-statement-result-types report them in terms of the underlying type. Parameters with user-defined domain types are not currently supported. As a workaround, cast the parameter to the underlying type. For example, if the type of $1 is a domain whose underlying type is integer, then replace $1 with ($1::integer).

For each type in the table above, the corresponding array type is also supported, using the pg-array structure. Use the = ANY syntax with an array parameter instead of dynamically constructing a SQL IN expression:

Examples:

> > (query-value pgc "select 1 in (1, 2, 3)")
> #t

> > (query-value pgc "select 1 = any ($1::integer[])"
> (list->pg-array (list 1 2 3)))

> #t

A list may be provided for an array parameter, in which case it is automatically converted using list->pg-array. The type annotation can be dropped when the array type can be inferred from the left-hand side.

Examples:

> > (query-value pgc "select 1 = any ($1)" (list 1 2 3))
> #t

> > (query-value pgc "select $1::integer = any ($2)"
> 1 (list 1 2 3))

> #t

> > (query-value pgc "select $1 = any ($2)" ; what type are we using?
> 1 (list 1 2 3))

> query-value: cannot convert to PostgreSQL string type: 1

PostgreSQL defines many other types, such as network addresses and row types. These are currently not supported, but support may be added in future versions of this library.

##### 4.1.2`` MySQL Types

This section applies to connections created with mysql-connect.

The following table lists the MySQL types known to this library, along with their corresponding Racket representations.

> MySQL type |  | Racket type
> 'integer |  | exact-integer?
> 'tinyint |  | exact-integer?
> 'smallint |  | exact-integer?
> 'mediumint |  | exact-integer?
> 'bigint |  | exact-integer?
> 'real |  | real?
> 'double |  | real?
> 'decimal |  | exact?
> 'varchar |  | string?
> 'date |  | sql-date?
> 'time |  | sql-time? or sql-day-time-interval?
> 'datetime |  | sql-timestamp?
> 'var-string |  | string?
> 'text |  | string?
> 'var-binary |  | bytes?
> 'blob |  | bytes?
> 'bit |  | sql-bits?
> 'geometry |  | geometry2d?

MySQL does not report specific parameter types for prepared queries, so they are instead assigned the pseudo-type 'any. Conversion of Racket values to parameters accepts strings, numbers (rational?—no infinities or NaN), bytes, SQL date/time structures (sql-date?, sql-time?, sql-timestamp?, and sql-day-time-interval?), bits (sql-bits?), and geometric values (geometry2d?). Numbers are sent as 64-bit signed integers, if possible, or as double-precision floating point numbers otherwise.

Fields of type CHAR or VARCHAR are typically reported as 'var-string, and fields of type BINARY or VARBINARY are typically reported as 'var-binary.

The MySQL time type represents time intervals, which may not correspond to times of day (for example, the interval may be negative or larger than 24 hours). In conversion from MySQL results to Racket values, those time values that represent times of day are converted to sql-time values; the rest are represented by sql-interval values.

The MySQL enum and set types are not supported. As a workaround, cast them to/from either integers or strings.

##### 4.1.3`` SQLite Types

This section applies to connections created with sqlite3-connect.

The following table lists the SQLite types known to this library, along with their corresponding Racket representations.

Unlike PostgreSQL and MySQL, SQLite does not enforce declared type constraints (with the exception of integer primary key) on columns. Rather, every SQLite value has an associated “storage class”.

> SQLite storage class |  | Racket type
> integer |  | exact-integer?
> real |  | real?
> text |  | string?
> blob |  | bytes?

SQLite does not report specific parameter and result types for prepared queries. Instead, they are assigned the pseudo-type 'any. Conversion of Racket values to parameters accepts strings, bytes, and real numbers.

An exact integer that cannot be represented as a 64-bit signed integer is converted as real, not integer.

Examples:

> > (expt 2 80)
> 1208925819614629174706176
> > (query-value slc "select ?" (expt 2 80))
> 1.2089258196146292e+24

##### 4.1.4`` ODBC Types

This section applies to connections created with odbc-connect or odbc-driver-connect.

The following table lists the ODBC types known to this library, along with their corresponding Racket representations.

> ODBC type |  | Racket type
> 'character |  | string?
> 'varchar |  | string?
> 'longvarchar |  | string?
> 'numeric |  | rational?
> 'decimal |  | rational?
> 'integer |  | exact-integer?
> 'tinyint |  | exact-integer?
> 'smallint |  | exact-integer?
> 'bigint |  | exact-integer?
> 'float |  | real?
> 'real |  | real?
> 'double |  | real?
> 'date |  | sql-date?
> 'time |  | sql-time?
> 'datetime |  | sql-timestamp?
> 'timestamp |  | sql-timestamp?
> 'binary |  | bytes?
> 'varbinary |  | bytes?
> 'longvarbinary |  | bytes?
> 'bit1 |  | boolean?

Not all ODBC drivers provide specific parameter type information for prepared queries. Some omit parameter type information entirely or, worse, assign all parameters a single type such as varchar. To avoid enforcing irrelevant type constraints in the last case, connections only attempt to fetch and enforce parameter types when the connection is made using the #:strict-parameter-type? option. Otherwise, the connection assigns all parameters the type 'unknown. (The 'unknown type is also used when specific parameter types are requested but are not available.) Conversion of Racket values to 'unknown parameters accepts strings, bytes, numbers (rational?—no infinities or NaN), booleans, and SQL date/time structures (sql-date?, sql-time?, and sql-timestamp?).

The ODBC type 'bit1 represents a single bit, unlike the standard SQL bit(N) type.

Interval types are not currently supported on ODBC.

#### 4.2`` SQL Data

This section describes data types for representing various SQL types that have no existing appropriate counterpart in Racket.

##### 4.2.1`` SQL NULL

SQL NULL is translated into the unique sql-null value.

> > value

> > sql-null : sql-null?

A special value used to represent NULL values in query results. The sql-null value may be recognized using eq?.

Example:

> > (query-value c "select NULL")
> #<sql-null>

> > procedure

> > (sql-null? x) → boolean?

> x : any/c

Returns #t if x is sql-null; #f otherwise.

> > procedure

> > (sql-null->false x) → any/c

> x : any/c

Returns #f if x is sql-null; otherwise returns x.

Examples:

> > (sql-null->false "apple")
> "apple"
> > (sql-null->false sql-null)
> #f
> > (sql-null->false #f)
> #f

> > procedure

> > (false->sql-null x) → any/c

> x : any/c

Returns sql-null if x is #f; otherwise returns x.

Examples:

> > (false->sql-null "apple")
> "apple"
> > (false->sql-null #f)
> #<sql-null>

##### 4.2.2`` Dates and Times

The DATE, TIME (WITH TIME ZONE and without), TIMESTAMP (WITH TIME ZONE and without), and INTERVAL SQL types are represented by the following structures.

See also Datetime Type Utilities for more functions on datetime values.

> > struct

> > (struct sql-date (year month day))

> year : exact-integer?
> month : (integer-in 0 12)
> day : (integer-in 0 31)

Represents a SQL date.

Dates with zero-valued month or day components are a MySQL extension.

> > struct

> > (struct sql-time (hour minute second nanosecond tz))

> hour : exact-nonnegative-integer?
> minute : exact-nonnegative-integer?
> second : exact-nonnegative-integer?
> nanosecond : exact-nonnegative-integer?
> tz : (or/c exact-integer? #f)

> > struct

> > (struct |  | sql-timestamp | ( | year
> > |  |  |  | month
> > |  |  |  | day
> > |  |  |  | hour
> > |  |  |  | minute
> > |  |  |  | second
> > |  |  |  | nanosecond
> > |  |  |  | tz))

> year : exact-nonnegative-integer?
> month : exact-nonnegative-integer?
> day : exact-nonnegative-integer?
> hour : exact-nonnegative-integer?
> minute : exact-nonnegative-integer?
> second : exact-nonnegative-integer?
> nanosecond : exact-nonnegative-integer?
> tz : (or/c exact-integer? #f)

Represents SQL times and timestamps.

The tz field indicates the time zone offset as the number of seconds east of GMT (as in SRFI 19). If tz is #f, the time or timestamp does not carry time zone information.

The sql-time and sql-timestamp structures store fractional seconds to nanosecond precision for compatibility with SRFI 19. Note, however, that database systems generally do not support nanosecond precision; PostgreSQL, for example, only supports microsecond precision.

Examples:

> > (query-value pgc "select date '25-dec-1980'")
> (sql-date 1980 12 25)
> > (query-value pgc "select time '7:30'")
> (sql-time 7 30 0 0 #f)
> > (query-value pgc "select timestamp 'epoch'")
> (sql-timestamp 1970 1 1 0 0 0 0 #f)
> > (query-value pgc "select timestamp with time zone 'epoch'")
> (sql-timestamp 1969 12 31 19 0 0 0 -18000)

Examples:

> > (query-value myc "select date('1980-12-25')")
> (sql-date 1980 12 25)
> > (query-value myc "select time('7:30')")
> (sql-time 7 30 0 0 #f)
> > (query-value myc "select from_unixtime(0)")
> (sql-timestamp 1969 12 31 19 0 0 0 #f)

> > struct

> > (struct |  | sql-interval | ( | years
> > |  |  |  | months
> > |  |  |  | days
> > |  |  |  | hours
> > |  |  |  | minutes
> > |  |  |  | seconds
> > |  |  |  | nanoseconds))

> years : exact-integer?
> months : exact-integer?
> days : exact-integer?
> hours : exact-integer?
> minutes : exact-integer?
> seconds : exact-integer?
> nanoseconds : exact-integer?

Represents lengths of time. Intervals are normalized to satisfy the following constraints:

- years and months have the same sign

- months ranges from -11 to 11

- days, hours, minutes, seconds, and nanoseconds all have the same sign

- hours ranges from -23 to 23

- minutes and seconds range from -59 to 59

- nanoseconds ranges from (- (sub1 #e1e9)) to (sub1 #e1e9)

That is, an interval consists of two groups of components: year-month and day-time, and normalization is done only within groups. In fact, the SQL standard recognizes those two types of intervals separately (see sql-year-month-interval? and sql-day-time-interval?, below), and does not permit combining them. Intervals such as 1 month 3 days are a PostgreSQL extension.

> > procedure

> > (sql-year-month-interval? x) → boolean?

> x : any/c

Returns #t if x is a sql-interval value where the days, hours, minutes, seconds, and nanoseconds fields are zero.

> > procedure

> > (sql-day-time-interval? x) → boolean?

> x : any/c

Returns #t if x is a sql-interval value where the years and months fields are zero.

> > procedure

> > (sql-interval->sql-time interval [failure]) → any

> interval : sql-interval?
> failure : any/c = (lambda () (error ....))

If interval is a day-time interval that represents a time of day, returns the corresponding sql-time value. In particular, the following must be true:

- hours, minutes, seconds, and nanoseconds must all be non-negative

- hours must be between 0 and 23

The corresponding constraints on minutes, etc are enforced by the constructor.

If interval is out of range, the failure value is called, if it is a procedure, or returned, otherwise.

> > procedure

> > (sql-time->sql-interval time) → sql-day-time-interval?

> time : sql-time?

Converts time to an interval. If time has time-zone information, it is ignored.

##### 4.2.3`` Bits

The BIT and BIT VARYING (VARBIT) SQL types are represented by sql-bits values.

> > procedure

> > (make-sql-bits len) → sql-bits?

> len : exact-nonnegative-integer?

Creates a new sql-bits value containing len zeros.

> > procedure

> > (sql-bits? v) → boolean?

> v : any/c

Returns #t if v is a sql-bits value, #f otherwise.

> > procedure

> > (sql-bits-length b) → exact-nonnegative-integer?

> b : sql-bits?

Returns the number of bits stored in b.

> > procedure

> > (sql-bits-ref b i) → boolean?

> b : sql-bits?
> i : exact-nonnegative-integer?

Returns the bit stored by b at index i as a boolean.

> > procedure

> > (sql-bits-set! b i v) → void?

> b : sql-bits?
> i : exact-nonnegative-integer?
> v : boolean?

Updates b, setting the bit at index i to v.

> > procedure

> > (sql-bits->list b) → (listof boolean?)

> b : sql-bits?

> > procedure

> > (sql-bits->string b) → string?

> b : sql-bits?

> > procedure

> > (list->sql-bits lst) → sql-bits?

> lst : (listof boolean?)

> > procedure

> > (string->sql-bits s) → sql-bits?

> s : string?

Converts a sql-bits value to or from its representation as a list or string.

Examples:

> > (sql-bits->list (string->sql-bits "1011"))
> '(#t #f #t #t)
> > (sql-bits->string (query-value pgc "select B'010110111'"))
> "010110111"

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