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planner: plan cache support subquery #13228

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Mar 20, 2023
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planner: plan cache support subquery #13228

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Update sql-prepared-plan-cache.md
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Merge branch 'plancache_subquery' of https://github.com/fzzf678/docs-…
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2 changes: 1 addition & 1 deletion sql-prepared-plan-cache.md
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Expand Up @@ -18,7 +18,7 @@ TiDB 优化器对这两类查询的处理是一样的：`Prepare` 时将参数

- `SELECT`、`UPDATE`、`INSERT`、`DELETE`、`Union`、`Intersect`、`Except` 以外的 SQL 语句；
- 访问分区表、临时表或访问表中包含生成列的查询；
- 包含子查询的查询，如 `select * from t where a > (select ...)`；
- 查询中包含非关联子查询或无法解关联的关联子查询，例如 `select * from t1 where t1.a > (select 1 from t2 where t2.b < 1)` 和 `select * from t1 where t1.a > (select a from t2 where t1.b > t2.b)` 分别是无法缓存的非关联子查询和关联子查询
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- 包含 `ignore_plan_cache` 这一 Hint 的查询，例如 `select /*+ ignore_plan_cache() */ * from t`；
- 包含除 `?` 外其他变量（即系统变量或用户自定义变量）的查询，例如 `select * from t where a>? and b>@x`；
- 查询包含无法被缓存函数。目前不能被缓存的函数有：`database()`、`current_user`、`current_role`、`user`、`connection_id`、`last_insert_id`、`row_count`、`version`、`like`；
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