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include limitation of LIKE when it works with non-binary collation (#15443) #15445

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Nov 16, 2023
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include limitation of LIKE when it works with non-binary collation (#15443) #15445

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82808d0
include limitation of LIKE with non-binary collation
songrijie Nov 16, 2023
7d11fb8
Update character-set-and-collation.md
songrijie Nov 16, 2023
4256b8f
Update character-set-gbk.md
songrijie Nov 16, 2023
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2 changes: 2 additions & 0 deletions character-set-and-collation.md
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Expand Up @@ -109,6 +109,8 @@ SHOW COLLATION;
> **警告：**
>
> TiDB 会错误地将 `latin1` 视为 `utf8` 的子集。当用户存储不同于 `latin1` 和 `utf8` 编码的字符时，可能会导致意外情况出现。因此强烈建议使用 `utf8mb4` 字符集。详情参阅 [TiDB #18955](https://github.com/pingcap/tidb/issues/18955)。
>
> 如果查询条件中包含对字符串前缀的 `LIKE` 过滤， 比如 `LIKE 'prefix%'`，并且该列被设置为非二进制排序规则（即排序规则的后缀不是以 `_bin` 结尾），那么 TiDB 优化器暂时无法把这个过滤条件转化为范围扫描 (Range Scan)，而是用全量扫描代替。因此这类 SQL 有可能造成超出预期的资源消耗。

> **注意：**
>
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2 changes: 2 additions & 0 deletions character-set-gbk.md
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Expand Up @@ -88,6 +88,8 @@ SHOW COLLATION WHERE CHARSET = 'gbk';

* 对于 `ENUM` 和 `SET` 类型中的二进制字符，TiDB 目前都会将其作为 `utf8mb4` 字符集处理。

* 如果查询条件中包含对字符串前缀的 `LIKE` 过滤，比如 `LIKE 'prefix%'`，并且该列被设置为 GBK 的排序规则（`gbk_bin` 或 `gbk_chinese_ci`），那么 TiDB 优化器暂时无法把这个过滤条件转化为范围扫描 (Range Scan)，而是用全量扫描代替。因此这类 SQL 有可能造成超出预期的资源消耗。

## 组件兼容性

* TiFlash 目前不支持 GBK 字符集。
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