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add instructions about connection collation #16423

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Feb 4, 2024
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add instructions about connection collation #16423

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add instructions about connection collation
YangKeao Feb 4, 2024
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qiancai Feb 4, 2024
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fix format errors reported by CI
qiancai Feb 4, 2024
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7 changes: 5 additions & 2 deletions character-set-and-collation.md
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Expand Up @@ -57,8 +57,6 @@ SELECT 'A' = 'a';
1 row in set (0.00 sec)
```

TiDB defaults to using a binary collation. This differs from MySQL, which uses a case-insensitive collation by default.

## Character sets and collations supported by TiDB

Currently, TiDB supports the following character sets:
Expand Down Expand Up @@ -117,6 +115,11 @@ SHOW COLLATION;
> **Note:**
>
> The default collations in TiDB (binary collations, with the suffix `_bin`) are different than [the default collations in MySQL](https://dev.mysql.com/doc/refman/8.0/en/charset-charsets.html) (typically general collations, with the suffix `_general_ci` or `_ai_ci`). This can cause incompatible behavior when specifying an explicit character set but relying on the implicit default collation to be chosen.
>
> However, the default collations in TiDB are also affected by the [connection collation](https://dev.mysql.com/doc/refman/8.0/en/charset-connection.html#charset-connection-system-variables) settings of your clients. For example, the MySQL 8.x client defaults to `utf8mb4_0900_ai_ci` as the connection collation for the `utf8mb4` character set.
>
> - Before TiDB v7.4.0, if your client uses `utf8mb4_0900_ai_ci` as the [connection collation](https://dev.mysql.com/doc/refman/8.0/en/charset-connection.html#charset-connection-system-variables), TiDB falls back to using the TiDB server default collation `utf8mb4_bin` because TiDB does not support the `utf8mb4_0900_ai_ci` collation.
> - Starting from v7.4.0, if your client uses `utf8mb4_0900_ai_ci` as the [connection collation](https://dev.mysql.com/doc/refman/8.0/en/charset-connection.html#charset-connection-system-variables), TiDB follows the client's configuration to use `utf8mb4_0900_ai_ci` as the default collation.

You can use the following statement to view the collations (under the [new framework for collations](#new-framework-for-collations)) that corresponds to the character set.

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