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sql-statements: update claims on optimizer/explain compatibility #10289

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Jun 29, 2022
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sql-statements: update claims on optimizer/explain compatibility #10289

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6 changes: 5 additions & 1 deletion mysql-compatibility.md
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Expand Up @@ -91,7 +91,11 @@ TiDB 主要使用 Prometheus 和 Grafana 来存储及查询相关的性能监控

### 查询计划

`EXPLAIN`/`EXPLAIN FOR` 输出格式、内容、权限设置与 MySQL 有比较大的差别，参见[理解 TiDB 执行计划](/explain-overview.md)。
TiDB 中，执行计划（`EXPLAIN` 和 `EXPLAIN FOR`）在输出格式、内容、权限设置方面与 MySQL 有较大差别。

MySQL 系统变量 `optimizer_switch` 在 TiDB 中是只读的，对查询计划没有影响。你还可以在 [optimizer hints](/optimizer-hints.md) 中使用与 MySQL 类似的语法，但可用的 hint 和实现原理可能会有所不同。

详情参见[理解 TiDB 执行计划](/explain-overview.md)。

### 内建函数

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2 changes: 1 addition & 1 deletion sql-statements/sql-statement-explain.md
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Expand Up @@ -246,7 +246,7 @@ The `xx.dot` is the result returned by the above statement.
## MySQL 兼容性

* `EXPLAIN` 的格式和 TiDB 中潜在的执行计划都与 MySQL 有很大不同。
* TiDB 不像 MySQL 那样支持 `EXPLAIN FORMAT = JSON`。
* TiDB 不支持 `FORMAT=JSON` 或 `FORMAT=TREE` 选项。

## `EXPLAIN FOR CONNECTION`

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