Skip to content

Latest commit

 

History

History
201 lines (152 loc) · 8.68 KB

character-set-support.md

File metadata and controls

201 lines (152 loc) · 8.68 KB
Raw
title summary category
Character Set Support
Learn about the supported character sets in TiDB.
user guide

Character Set Support

A character set is a set of symbols and encodings. A collation is a set of rules for comparing characters in a character set.

Currently, TiDB supports the following character sets:

mysql> SHOW CHARACTER SET;
+---------|---------------|-------------------|--------+
| Charset | Description   | Default collation | Maxlen |
+---------|---------------|-------------------|--------+
| utf8    | UTF-8 Unicode | utf8_bin          |      3 |
| utf8mb4 | UTF-8 Unicode | utf8mb4_bin       |      4 |
| ascii   | US ASCII      | ascii_bin         |      1 |
| latin1  | Latin1        | latin1_bin        |      1 |
| binary  | binary        | binary            |      1 |
+---------|---------------|-------------------|--------+
5 rows in set (0.00 sec)

Note: In TiDB, utf8 is treated as utf8mb4.

Each character set has at least one collation. Most of the character sets have several collations. You can use the following statement to display the available character sets:

mysql> SHOW COLLATION WHERE Charset = 'latin1';
+-------------------|---------|------|---------|----------|---------+
| Collation         | Charset | Id   | Default | Compiled | Sortlen |
+-------------------|---------|------|---------|----------|---------+
| latin1_german1_ci | latin1  |    5 |         | Yes      |       1 |
| latin1_swedish_ci | latin1  |    8 | Yes     | Yes      |       1 |
| latin1_danish_ci  | latin1  |   15 |         | Yes      |       1 |
| latin1_german2_ci | latin1  |   31 |         | Yes      |       1 |
| latin1_bin        | latin1  |   47 |         | Yes      |       1 |
| latin1_general_ci | latin1  |   48 |         | Yes      |       1 |
| latin1_general_cs | latin1  |   49 |         | Yes      |       1 |
| latin1_spanish_ci | latin1  |   94 |         | Yes      |       1 |
+-------------------|---------|------|---------|----------|---------+
8 rows in set (0.00 sec)

The latin1 collations have the following meanings:

Collation Meaning
latin1_bin Binary according to latin1 encoding
latin1_danish_ci Danish/Norwegian
latin1_general_ci Multilingual (Western European)
latin1_general_cs Multilingual (ISO Western European), case sensitive
latin1_german1_ci German DIN-1 (dictionary order)
latin1_german2_ci German DIN-2 (phone book order)
latin1_spanish_ci Modern Spanish
latin1_swedish_ci Swedish/Finnish

Each character set has a default collation. For example, the default collation for utf8 is utf8_bin.

Note: The collations in TiDB are case sensitive.

Collation naming conventions

The collation names in TiDB follow these conventions:

  • The prefix of a collation is its corresponding character set, generally followed by one or more suffixes indicating other collation characteristic. For example, utf8_general_ci and latin1_swedish_ci are collations for the utf8 and latin1 character sets, respectively. The binary character set has a single collation, also named binary, with no suffixes.

  • A language-specific collation includes a language name. For example, utf8_turkish_ci and utf8_hungarian_ci sort characters for the utf8 character set using the rules of Turkish and Hungarian, respectively.

  • Collation suffixes indicate whether a collation is case and accent sensitive, or binary. The following table shows the suffixes used to indicate these characteristics.

    Suffix Meaning
    _ai Accent insensitive
    _as Accent sensitive
    _ci Case insensitive
    _cs Case sensitive
    _bin Binary

Note: Currently, TiDB only supports some of the collations in the above table.

Database character set and collation

Each database has a character set and a collation. You can use the CREATE DATABASE statement to specify the database character set and collation:

CREATE DATABASE db_name
    [[DEFAULT] CHARACTER SET charset_name]
    [[DEFAULT] COLLATE collation_name]

Where DATABASE can be replaced with SCHEMA.

Different databases can use different character sets and collations. Use the character_set_database and collation_database to see the character set and collation of the current database:

mysql> create schema test1 character set utf8 COLLATE uft8_general_ci;
Query OK, 0 rows affected (0.09 sec)

mysql> use test1;
Database changed
mysql> SELECT @@character_set_database, @@collation_database;
+--------------------------|----------------------+
| @@character_set_database | @@collation_database |
+--------------------------|----------------------+
| utf8                     | uft8_general_ci      |
+--------------------------|----------------------+
1 row in set (0.00 sec)

mysql> create schema test2 character set latin1 COLLATE latin1_general_ci;
Query OK, 0 rows affected (0.09 sec)

mysql> use test2;
Database changed
mysql> SELECT @@character_set_database, @@collation_database;
+--------------------------|----------------------+
| @@character_set_database | @@collation_database |
+--------------------------|----------------------+
| latin1                   | latin1_general_ci    |
+--------------------------|----------------------+
1 row in set (0.00 sec)

You can also see the two values in INFORMATION_SCHEMA:

SELECT DEFAULT_CHARACTER_SET_NAME, DEFAULT_COLLATION_NAME
FROM INFORMATION_SCHEMA.SCHEMATA WHERE SCHEMA_NAME = 'db_name';

Table character set and collation

You can use the following statement to specify the character set and collation for tables:

CREATE TABLE tbl_name (column_list)
    [[DEFAULT] CHARACTER SET charset_name]
    [COLLATE collation_name]]

ALTER TABLE tbl_name
    [[DEFAULT] CHARACTER SET charset_name]
    [COLLATE collation_name]

For example:

mysql> CREATE TABLE t1(a int) CHARACTER SET utf8 COLLATE utf8_general_ci;
Query OK, 0 rows affected (0.08 sec)

The table character set and collation are used as the default values for column definitions if the column character set and collation are not specified in individual column definitions.

Column character set and collation

See the following table for the character set and collation syntax for columns:

col_name {CHAR | VARCHAR | TEXT} (col_length)
    [CHARACTER SET charset_name]
    [COLLATE collation_name]

col_name {ENUM | SET} (val_list)
    [CHARACTER SET charset_name]
    [COLLATE collation_name]

Connection character sets and collations

  • The server character set and collation are the values of the character_set_server and collation_server system variables.

  • The character set and collation of the default database are the values of the character_set_database and collation_database system variables. You can use character_set_connection and collation_connection to specify the character set and collation for each connection. The character_set_client variable is to set the client character set. Before returning the result, the character_set_results system variable indicates the character set in which the server returns query results to the client, including the metadata of the result.

You can use the following statement to specify a particular collation that is related to the client:

  • SET NAMES 'charset_name' [COLLATE 'collation_name']

    SET NAMES indicates what character set the client will use to send SQL statements to the server. SET NAMES utf8 indicates that all the requests from the client use utf8, as well as the results from the server.

    The SET NAMES 'charset_name' statement is equivalent to the following statement combination:

    SET character_set_client = charset_name;
SET character_set_results = charset_name;
SET character_set_connection = charset_name;

    COLLATE is optional, if absent, the default collation of the charset_name is used.

  • SET CHARACTER SET 'charset_name'

    Similar to SET NAMES, the SET NAMES 'charset_name' statement is equivalent to the following statement combination:

    SET character_set_client = charset_name;
SET character_set_results = charset_name;
SET collation_connection = @@collation_database;

For more information, see Connection Character Sets and Collations in MySQL.