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 NULL
sql-null
sql-null?
sql-null->false
false->sql-null
4.2.2 Dates and times
sql-date
sql-time
sql-timestamp
sql-datetime->srfi-date
srfi-date->sql-date
srfi-date->sql-time
srfi-date->sql-time-tz
srfi-date->sql-timestamp
srfi-date->sql-timestamp-tz
sql-interval
sql-year-month-interval?
sql-day-time-interval?
sql-day-time-interval->seconds
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

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 Scheme 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 (planet ryanc/db:1:5/util/geometry) and (planet ryanc/db:1:5/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).

PostgreSQL defines many other types, such as network addresses, array types, 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 package, 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?

'var-string

string? or bytes?, but see below

'date

sql-date?

'time

sql-time? or sql-day-time-interval?

'datetime

sql-timestamp?

'blob

bytes?

'tinyblob

bytes?

'mediumblob

bytes?

'longblob

bytes?

'bit

sql-bits?

'geometry

geometry2d?

MySQL does not report specific parameter types for prepared queries, instead assigning them the type var-string. Consequently, conversion of Racket values to var-string 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?).

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 package, 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 pseudotype '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 package, 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 NULL

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

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>

(sql-null? x)  boolean?
  x : any/c
Returns #t if x is sql-null; #f otherwise.

(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

(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.

(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 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 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)

Converts between this library’s date and time values and SRFI 19’s date values (see srfi/19). SRFI dates store more information than SQL dates and times, so converting a SQL time to a SRFI date, for example, puts zeroes in the year, month, and day fields.

Examples:

> (sql-datetime->srfi-date
   (query-value pgc "select time '7:30'"))

(tm:date 0 0 30 7 0 0 0 0)

> (sql-datetime->srfi-date
   (query-value pgc "select date '25-dec-1980'"))

(tm:date 0 0 0 0 25 12 1980 0)

> (sql-datetime->srfi-date
   (query-value pgc "select timestamp 'epoch'"))

(tm:date 0 0 0 0 1 1 1970 0)

(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.

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

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

Returns the length of interval in seconds.

(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.

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.

Creates a new sql-bits value containing len zeros.

(sql-bits? v)  boolean?
  v : any/c
Returns #t if v is a sql-bits value, #f otherwise.

Returns the number of bits stored in b.

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

(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.

(sql-bits->list b)  (listof boolean?)
  b : sql-bits?
(sql-bits->string b)  string?
  b : sql-bits?
(list->sql-bits lst)  sql-bits?
  lst : (listof boolean?)
(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"