CAST

Convert a value to a specific data type. This function explicitly converts a value from one type to another, such as string to integer.

Syntax

CAST(expr AS type)

Description

The CAST() function takes a value of one type and produces a value of another type, similar to the CONVERT() function.

The type can be one of the following values:

• BINARY

• CHAR

• DATE

• DATETIME

• [DECIMAL (M[,D])]

• DOUBLE

• FLOAT

• INTEGER

  • Short for SIGNED INTEGER

• SIGNED [INTEGER]

• UNSIGNED [INTEGER]

• TIME

• VARCHAR

The main difference between CAST and CONVERT() is that CONVERT(expr,type) is ODBC syntax while CAST(expr as type) and CONVERT(... USING ...) are SQL92 syntax.

You can use the CAST() function with the INTERVAL keyword.

This introduced an incompatibility with previous versions of MariaDB, and all versions of MySQL (see the example below).

Examples

Simple Casts

SELECT CAST("abc" AS BINARY);
SELECT CAST("1" AS UNSIGNED INTEGER);
SELECT CAST(123 AS CHAR CHARACTER SET utf8)

Note that when one casts to CHAR without specifying the character set, the collation_connection character set collation will be used. When used with CHAR CHARACTER SET, the default collation for that character set will be used.

SELECT COLLATION(CAST(123 AS CHAR));
+------------------------------+
| COLLATION(CAST(123 AS CHAR)) |
+------------------------------+
| latin1_swedish_ci            |
+------------------------------+

SELECT COLLATION(CAST(123 AS CHAR CHARACTER SET utf8));
+-------------------------------------------------+
| COLLATION(CAST(123 AS CHAR CHARACTER SET utf8)) |
+-------------------------------------------------+
| utf8_general_ci                                 |
+-------------------------------------------------+

If you also want to change the collation, you have to use the COLLATE operator:

SELECT COLLATION(CAST(123 AS CHAR CHARACTER SET utf8) 
  COLLATE utf8_unicode_ci);
+-------------------------------------------------------------------------+
| COLLATION(CAST(123 AS CHAR CHARACTER SET utf8) COLLATE utf8_unicode_ci) |
+-------------------------------------------------------------------------+
| utf8_unicode_ci                                                         |
+-------------------------------------------------------------------------+

Using CAST() to order an ENUM field as a CHAR rather than the internal numerical value:

CREATE TABLE enum_list (enum_field enum('c','a','b'));

INSERT INTO enum_list (enum_field) 
VALUES('c'),('a'),('c'),('b');

SELECT * FROM enum_list 
ORDER BY enum_field;
+------------+
| enum_field |
+------------+
| c          |
| c          |
| a          |
| b          |
+------------+

SELECT * FROM enum_list 
ORDER BY CAST(enum_field AS CHAR);
+------------+
| enum_field |
+------------+
| a          |
| b          |
| c          |
| c          |
+------------+

The following will trigger warnings, since x'aa' and 'X'aa' doesn't behave as a number. In all versions of MySQL, no warnings are triggered since they did erroneously behave as a number:

SELECT CAST(0xAA AS UNSIGNED), CAST(x'aa' AS UNSIGNED), CAST(X'aa' AS UNSIGNED);
+------------------------+-------------------------+-------------------------+
| CAST(0xAA AS UNSIGNED) | CAST(x'aa' AS UNSIGNED) | CAST(X'aa' AS UNSIGNED) |
+------------------------+-------------------------+-------------------------+
|                    170 |                       0 |                       0 |
+------------------------+-------------------------+-------------------------+
1 row in set, 2 warnings (0.00 sec)

Warning (Code 1292): Truncated incorrect INTEGER value: '\xAA'
Warning (Code 1292): Truncated incorrect INTEGER value: '\xAA'

Casting to Intervals

SELECT CAST(2019-01-04 AS INTERVAL DAY_SECOND(2)) AS "Cast";

+-------------+
| Cast        |
+-------------+
| 00:20:14.00 |
+-------------+

See Also

• Supported data types

• Microseconds in MariaDB

• String literals

• COLLATION()

• CONVERT()

_{This page is licensed: GPLv2, originally from fill_help_tables.sql}