Character Set and Collation Overview

What are character sets and collations

A character set is a set of characters while a collation is the rules for comparing and sorting a particular character set.

For example, a subset of a character set could consist of the letters A, B and C. A default collation could define these as appearing in an ascending order of A, B, C.

If we consider different case characters, more complexity is added. A binary collation would evaluate the characters A and a differently, ordering them in a particular way. A case-insensitive collation would evaluate A and a equivalently, while the German phone book collation evaluates the characters ue and ü equivalently.

A character set can have many collations associated with it, while each collation is only associated with one character set. In MariaDB, the character set name is always part of the collation name. For example, the latin1_german1_ci collation applies only to the latin1 character set. Each character set also has one default collation. The latin1 default collation is latin1_swedish_ci.

As an example, by default, the character y comes between x and z, while in Lithuanian, it's sorted between i and k. Similarly, the German phone book order is different to the German dictionary order, so while they share the same character set, the collation is different.

Viewing character sets and collations

In MariaDB, the default character set is latin1, and the default collation is latin1_swedish_ci (however this may differ in some distros, see for example Differences in MariaDB in Debian). You can view a full list of character sets and collations supported by MariaDB at Supported Character Sets and Collations, or see what's supported on your server with the SHOW CHARACTER SET and SHOW COLLATION commands.

By default, A comes before Z, so the following evaluates to true:

 SELECT "A" < "Z";
+-----------+
| "A" < "Z" |
+-----------+
|         1 |
+-----------+

By default, comparisons are case-insensitive:

SELECT "A" < "a", "A" = "a";
+-----------+-----------+
| "A" < "a" | "A" = "a" |
+-----------+-----------+
|         0 |         1 |
+-----------+-----------+

Changing character sets and collations

Character sets and collations can be set from the server level right down to the column level, as well as for client-server communication.

For example, ue and ü are by default evaluated differently.

SELECT 'Mueller' = 'Müller';
+----------------------+
| 'Müller' = 'Mueller' |
+----------------------+
|                    0 |
+----------------------+

By using the collation_connection system variable to change the connection character set to latin1_german2_ci, or German phone book, the same two characters will evaluate as equivalent.

SET collation_connection = latin1_german2_ci;

SELECT 'Mueller' = 'Müller';
+-----------------------+
| 'Mueller' = 'Müller'  |
+-----------------------+
|                     1 |
+-----------------------+

See Setting Character Sets and Collations for more.

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