Umesh Chandra

MySQL supports SQL data types in several categories: numeric types, date and time types, string (character and byte) types, spatial types, and the JSON data type. This provides an overview and more detailed description of the properties of the types in each category, and a summary of the data type storage requirements.

In SQL we have

• Numeric Data Types
• Date and Time Data Types
• String Data Types
• Spatial Data Types
• The JSON Data Types
• Data Type Default Values

Numeric Data Types:

MySQL supports all standard SQL numeric data types. These types include the exact numeric data types (INTEGER, SMALLINT, DECIMAL, and NUMERIC), as well as the approximate numeric data types (FLOAT, REAL, and DOUBLE PRECISION). The keyword INT is a synonym for INTEGER, and the keywords DEC and FIXED are synonyms for DECIMAL. MySQL treats DOUBLE as a synonym for DOUBLE PRECISION (a nonstandard extension). MySQL also treats REAL as a synonym for DOUBLE PRECISION (a nonstandard variation), unless the REAL_AS_FLOAT SQL mode is enabled.

• BOOL, BOOLEAN

mysql> SELECT IF(0, 'true', 'false');
+------------------------+
| IF(0, 'true', 'false') |
+------------------------+
| false                  |
+------------------------+

mysql> SELECT IF(1, 'true', 'false');
+------------------------+
| IF(1, 'true', 'false') |
+------------------------+
| true                   |
+------------------------+

mysql> SELECT IF(2, 'true', 'false');
+------------------------+
| IF(2, 'true', 'false') |
+------------------------+
| true                   |
+------------------------+

• SMALLINT[(M)] [UNSIGNED] [ZEROFILL]A small integer. The signed range is -32768 to 32767. The unsigned range is 0 to 65535.
• MEDIUMINT[(M)] [UNSIGNED] [ZEROFILL]A medium-sized integer. The signed range is -8388608 to 8388607. The unsigned range is 0 to 16777215.
• INT[(M)] [UNSIGNED] [ZEROFILL]A normal-size integer. The signed range is -2147483648 to 2147483647. The unsigned range is 0 to 4294967295.
• INTEGER[(M)] [UNSIGNED] [ZEROFILL]This type is a synonym for INT.
• BIGINT[(M)] [UNSIGNED] [ZEROFILL]A large integer. The signed range is -9223372036854775808 to 9223372036854775807. The unsigned range is 0 to 18446744073709551615.SERIAL is an alias for BIGINT UNSIGNED NOT NULL AUTO_INCREMENT UNIQUE.

Integer Types (Exact Value) – INTEGER, INT, SMALLINT, TINYINT, MEDIUMINT, BIGINT

MySQL supports the SQL standard integer types INTEGER (or INT) and SMALLINT. As an extension to the standard, MySQL also supports the integer types TINYINT, MEDIUMINT, and BIGINT. The following table shows the required storage and range for each integer type.

Table 11.1 Required Storage and Range for Integer Types Supported by MySQL

Fixed-Point Types (Exact Value) – DECIMAL, NUMERIC

The DECIMAL and NUMERIC types store exact numeric data values. These types are used when it is important to preserve exact precision, for example with monetary data. In MySQL, NUMERIC is implemented as DECIMAL, so the following remarks about DECIMAL apply equally to NUMERIC.

In a DECIMAL column declaration, the precision and scale can be (and usually is) specified. For example:

salary DECIMAL(5,2)

Out-of-Range and Overflow Handling

When MySQL stores a value in a numeric column that is outside the permissible range of the column data type, the result depends on the SQL mode in effect at the time:

• If strict SQL mode is enabled, MySQL rejects the out-of-range value with an error, and the insert fails, in accordance with the SQL standard.
• If no restrictive modes are enabled, MySQL clips the value to the appropriate endpoint of the column data type range and stores the resulting value instead.When an out-of-range value is assigned to an integer column, MySQL stores the value representing the corresponding endpoint of the column data type range.When a floating-point or fixed-point column is assigned a value that exceeds the range implied by the specified (or default) precision and scale, MySQL stores the value representing the corresponding endpoint of that range.

Suppose that a table t1 has this definition:

CREATE TABLE t1 (i1 TINYINT, i2 TINYINT UNSIGNED);

With strict SQL mode enabled, an out of range error occurs:

mysql> SET sql_mode = 'TRADITIONAL';
mysql> INSERT INTO t1 (i1, i2) VALUES(256, 256);
ERROR 1264 (22003): Out of range value for column 'i1' at row 1
mysql> SELECT * FROM t1;
Empty set (0.00 sec)

With strict SQL mode not enabled, clipping with warnings occurs:

mysql> SET sql_mode = '';
mysql> INSERT INTO t1 (i1, i2) VALUES(256, 256);
mysql> SHOW WARNINGS;
+---------+------+---------------------------------------------+
| Level   | Code | Message                                     |
+---------+------+---------------------------------------------+
| Warning | 1264 | Out of range value for column 'i1' at row 1 |
| Warning | 1264 | Out of range value for column 'i2' at row 1 |
+---------+------+---------------------------------------------+
mysql> SELECT * FROM t1;
+------+------+
| i1   | i2   |
+------+------+
|  127 |  255 |
+------+------+

Overflow during numeric expression evaluation results in an error. For example, the largest signed BIGINT value is 9223372036854775807, so the following expression produces an error:

mysql> SELECT 9223372036854775807 + 1;
ERROR 1690 (22003): BIGINT value is out of range in '(9223372036854775807 + 1)'

To enable the operation to succeed in this case, convert the value to unsigned;

mysql> SELECT CAST(9223372036854775807 AS UNSIGNED) + 1;
+-------------------------------------------+
| CAST(9223372036854775807 AS UNSIGNED) + 1 |
+-------------------------------------------+
|                       9223372036854775808 |
+-------------------------------------------+

Whether overflow occurs depends on the range of the operands, so another way to handle the preceding expression is to use exact-value arithmetic because DECIMAL values have a larger range than integers:

mysql> SELECT 9223372036854775807.0 + 1;
+---------------------------+
| 9223372036854775807.0 + 1 |
+---------------------------+
|     9223372036854775808.0 |
+---------------------------+

Subtraction between integer values, where one is of type UNSIGNED, produces an unsigned result by default. If the result would otherwise have been negative, an error results:

mysql> SET sql_mode = '';
Query OK, 0 rows affected (0.00 sec)

mysql> SELECT CAST(0 AS UNSIGNED) - 1;
ERROR 1690 (22003): BIGINT UNSIGNED value is out of range in '(cast(0 as unsigned) - 1)'

If the NO_UNSIGNED_SUBTRACTION SQL mode is enabled, the result is negative:

mysql> SET sql_mode = 'NO_UNSIGNED_SUBTRACTION';
mysql> SELECT CAST(0 AS UNSIGNED) - 1;
+-------------------------+
| CAST(0 AS UNSIGNED) - 1 |
+-------------------------+
|                      -1 |
+-------------------------+

If the result of such an operation is used to update an UNSIGNED integer column, the result is clipped to the maximum value for the column type, or clipped to 0 if NO_UNSIGNED_SUBTRACTION is enabled. If strict SQL mode is enabled, an error occurs and the column remains unchanged.