CAST

Description

The CAST() function converts a value (of any type) into the specified datatype.

Syntax

> CAST(value AS datatype)

Parameter Values

Parameter

Description

value

Required. The value to convert

datatype

Required. The datatype to convert to

Currently, cast can support following conversion:

  • Conversion between numeric types, mainly including SIGNED, UNSIGNED, FLOAT, and DOUBLE type.

  • Numeric types to character CHAR type.

  • Numeric character types to numerical types(negative into SIGNED).

  • Time type (including Date, Datetime, Timestamp, and Time) is converted to INT type, with decimal point rounding

  • Time types (including Date, Datetime, Timestamp, and Time) are converted to fixed-point types with decimal places

A detailed data type conversion rule can be refered to Data Conversion Rule.

Examples

drop table if exists t1;
CREATE TABLE t1 (a int,b float,c char(1),d varchar(15));
INSERT INTO t1 VALUES (1,1.5,'1','-2');

mysql> SELECT CAST(a AS FLOAT) a_cast,CAST(b AS UNSIGNED) b_cast,CAST(c AS SIGNED) c_cast, CAST(d AS SIGNED) d_cast from t1;
+--------+--------+--------+--------+
| a_cast | b_cast | c_cast | d_cast |
+--------+--------+--------+--------+
| 1.0000 |      1 |      1 |     -2 |
+--------+--------+--------+--------+

mysql> SELECT CAST(a AS CHAR) a_cast, CAST(b AS CHAR) b_cast,CAST(c AS DOUBLE) c_cast, CAST(d AS FLOAT) d_cast from t1;
+--------+--------+--------+---------+
| a_cast | b_cast | c_cast | d_cast  |
+--------+--------+--------+---------+
| 1      | 1.5    | 1.0000 | -2.0000 |
+--------+--------+--------+---------+

Constraints

  • Non-numeric character types cannot be converted to numeric types.

  • Casting a DATETIME type value to CHAR may fail in some cases (CAST(NOW() AS CHAR) works but CAST(a_datetime_column AS CHAR) may not).