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Update the related variable description for CREATE INDEX (#6588) #6608

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ti-chi-bot merged 2 commits into from
Jul 5, 2021
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Update the related variable description for CREATE INDEX (#6588) #6608

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e196421
This is an automated cherry-pick of #6588
qiancai Jul 5, 2021
13631ca
Update sql-statement-create-index.md
qiancai Jul 5, 2021
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4 changes: 2 additions & 2 deletions sql-statements/sql-statement-create-index.md
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Expand Up @@ -185,9 +185,9 @@ CREATE INDEX idx ON t ((lower(name)));

表达式索引的语法和限制与 MySQL 相同，是通过将索引建立在隐藏的虚拟生成列 (generated virtual column) 上来实现的。因此所支持的表达式继承了虚拟生成列的所有[限制](/generated-columns.md#生成列的局限性)。目前，建立了索引的表达式只有在 `FIELD` 子句、`WHERE` 子句和 `ORDER BY` 子句中时，优化器才能使用表达式索引。后续将支持 `GROUP BY` 子句。

## 相关 session 变量
## 相关系统变量

和 `CREATE INDEX` 语句相关的全局变量有 `tidb_ddl_reorg_worker_cnt`，`tidb_ddl_reorg_batch_size` 和 `tidb_ddl_reorg_priority`，具体可以参考[系统变量](/system-variables.md#tidb_ddl_reorg_worker_cnt)。
和 `CREATE INDEX` 语句相关的系统变量有 `tidb_ddl_reorg_worker_cnt` 、`tidb_ddl_reorg_batch_size` 和 `tidb_ddl_reorg_priority`，具体可以参考[系统变量](/system-variables.md#tidb_ddl_reorg_worker_cnt)。

## MySQL 兼容性

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