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sql: Document character sets / collations #628

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Sep 27, 2018
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sql: Document character sets / collations #628

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26 changes: 13 additions & 13 deletions sql/system-database.md
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Expand Up @@ -42,29 +42,29 @@ To be compatible with MySQL, TiDB supports INFORMATION\_SCHEMA tables. Some thir

### CHARACTER\_SETS table

The CHARACTER\_SETS table provides information about character sets. But it contains dummy data. By default, TiDB only supports utf8mb4.
The CHARACTER\_SETS table provides information about [character sets](character-set-support.md). The default character set in TiDB is `utf8`, which behaves similar to `utf8mb4` in MySQL. Additional character sets in this table are included for compatibility with MySQL:

```sql
mysql> select * from CHARACTER_SETS;
+--------------------|----------------------|-----------------------|--------+
| CHARACTER_SET_NAME | DEFAULT_COLLATE_NAME | DESCRIPTION | MAXLEN |
+--------------------|----------------------|-----------------------|--------+
| ascii | ascii_general_ci | US ASCII | 1 |
| binary | binary | Binary pseudo charset | 1 |
| latin1 | latin1_swedish_ci | cp1252 West European | 1 |
| utf8 | utf8_general_ci | UTF-8 Unicode | 3 |
| utf8mb4 | utf8mb4_general_ci | UTF-8 Unicode | 4 |
+--------------------|----------------------|-----------------------|--------+
mysql> SELECT * FROM character_sets;
+--------------------+----------------------+---------------+--------+
| CHARACTER_SET_NAME | DEFAULT_COLLATE_NAME | DESCRIPTION | MAXLEN |
+--------------------+----------------------+---------------+--------+
| utf8 | utf8_bin | UTF-8 Unicode | 3 |
| utf8mb4 | utf8mb4_bin | UTF-8 Unicode | 4 |
| ascii | ascii_bin | US ASCII | 1 |
| latin1 | latin1_bin | Latin1 | 1 |
| binary | binary | binary | 1 |
+--------------------+----------------------+---------------+--------+
5 rows in set (0.00 sec)
```

### COLLATIONS table

The COLLATIONS table is similar to the CHARACTER\_SETS table.
The COLLATIONS table provides a list of collations that correspond to character sets in the CHARACTER\_SETS table. Currently this table is included only for compatibility with MySQL, as TiDB only supports binary collation.

### COLLATION\_CHARACTER\_SET\_APPLICABILITY table

NULL.
This table maps collations to the applicable character set name. Similar to the collations table, it is included only for compatibility with MySQL.

### COLUMNS table

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