The Ultimate Guide to High Availability with MariaDB

Numeric Data Type Overview

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Contents

  1. SIGNED, UNSIGNED and ZEROFILL
    1. Examples
  2. Range
    1. Examples
  3. Auto_increment

There are a number of numeric data types:

See the specific articles for detailed information on each.

SIGNED, UNSIGNED and ZEROFILL

Most numeric types can be defined as SIGNED, UNSIGNED or ZEROFILL, for example:

TINYINT[(M)] [SIGNED | UNSIGNED | ZEROFILL]

If SIGNED, or no attribute, is specified, a portion of the numeric type will be reserved for the sign (plus or minus). For example, a TINYINT SIGNED can range from -128 to 127.

If UNSIGNED is specified, no portion of the numeric type is reserved for the sign, so for integer types range can be larger. For example, a TINYINT UNSIGNED can range from 0 to 255. Floating point and fixed-point types also can be UNSIGNED, but this only prevents negative values from being stored and doesn't alter the range.

If ZEROFILL is specified, the column will be set to UNSIGNED and the spaces used by default to pad the field are replaced with zeros. ZEROFILL is ignored in expressions or as part of a UNION. ZEROFILL is a non-standard MySQL and MariaDB enhancement.

Note that although the preferred syntax indicates that the attributes are exclusive, more than one attribute can be specified.

Until MariaDB 10.2.7 (MDEV-8659), any combination of the attributes could be used in any order, with duplicates. In this case:

  • the presence of ZEROFILL makes the column UNSIGNED ZEROFILL.
  • the presence of UNSIGNED makes the column UNSIGNED.

From MariaDB 10.2.8, only the following combinations are supported:

  • SIGNED
  • UNSIGNED
  • ZEROFILL
  • UNSIGNED ZEROFILL
  • ZEROFILL UNSIGNED

The latter two should be replaced with simply ZEROFILL, but are still accepted by the parser.

Examples

CREATE TABLE zf (
  i1 TINYINT SIGNED,
  i2 TINYINT UNSIGNED,
  i3 TINYINT ZEROFILL
);

INSERT INTO zf VALUES (2,2,2);

SELECT * FROM zf;
+------+------+------+
| i1   | i2   | i3   |
+------+------+------+
|    2 |    2 |  002 |
+------+------+------+

Range

When attempting to add a value that is out of the valid range for the numeric type, MariaDB will react depending on the strict SQL_MODE setting.

If strict_mode has been set (the default from MariaDB 10.2.4), MariaDB will return an error.

If strict_mode has not been set (the default until MariaDB 10.2.3), MariaDB will adjust the number to fit in the field, returning a warning.

Examples

With strict_mode set:

SHOW VARIABLES LIKE 'sql_mode';
+---------------+-------------------------------------------------------------------------------------------+
| Variable_name | Value                                                                                     |
+---------------+-------------------------------------------------------------------------------------------+
| sql_mode      | STRICT_TRANS_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |
+---------------+-------------------------------------------------------------------------------------------+

CREATE TABLE ranges (i1 TINYINT, i2 SMALLINT, i3 TINYINT UNSIGNED);

INSERT INTO ranges VALUES (257,257,257);
ERROR 1264 (22003): Out of range value for column 'i1' at row 1

SELECT * FROM ranges;
Empty set (0.10 sec)

With strict_mode unset:

SHOW VARIABLES LIKE 'sql_mode%';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| sql_mode      |       |
+---------------+-------+

CREATE TABLE ranges (i1 TINYINT, i2 SMALLINT, i3 TINYINT UNSIGNED);

INSERT INTO ranges VALUES (257,257,257);
Query OK, 1 row affected, 2 warnings (0.00 sec)

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 'i3' at row 1 |
+---------+------+---------------------------------------------+
2 rows in set (0.00 sec)

SELECT * FROM ranges;
+------+------+------+
| i1   | i2   | i3   |
+------+------+------+
|  127 |  257 |  255 |
+------+------+------+

Auto_increment

The AUTO_INCREMENT attribute can be used to generate a unique identity for new rows. For more details, see auto_increment.

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