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add some point desc #11454

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merged 3 commits into from
Sep 30, 2022
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add some point desc #11454

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bd4055e
add some point desc
glkappe Sep 29, 2022
d720f4a
Update statistics.md
AilinKid Sep 30, 2022
9427b08
fix format
Oreoxmt Sep 30, 2022
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16 changes: 7 additions & 9 deletions statistics.md
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Expand Up @@ -13,19 +13,17 @@ TiDB 使用统计信息来决定[索引的选择](/choose-index.md)。变量 `ti
>
> - 如果 ANALYZE 语句是手动执行的，请手动 analyze 每张需要的表：
>
> {{< copyable "sql" >}}
>
> ```sql
> select distinct(concat('ANALYZE ',table_schema, '.', table_name,';')) from information_schema.tables, mysql.stats_histograms where stats_ver = 2 and table_id = tidb_table_id ;
> ```
> ```sql
> SELECT DISTINCT(CONCAT('ANALYZE TABLE', table_schema, '.', table_name, ';')) FROM information_schema.tables, mysql.stats_histograms WHERE stats_ver = 2 AND table_id = tidb_table_id;
> ```
>
> - 如果 ANALYZE 语句是开启了自动 analyze 后 TiDB 自动执行的，请使用以下 SQL 语句生成 DROP STATS 的语句并执行：
>
> {{< copyable "sql" >}}
>
> ```sql
> select distinct(concat('DROP STATS ',table_schema, '.', table_name,';')) from information_schema.tables, mysql.stats_histograms where stats_ver = 2 and table_id = tidb_table_id ;
> ```
> ```sql
> SELECT DISTINCT(CONCAT('DROP STATS ', table_schema, '.', table_name, ';')) FROM information_schema.tables, mysql.stats_histograms WHERE stats_ver = 2 AND table_id = tidb_table_id;
> ```

两种版本中，TiDB 维护的统计信息如下：

Expand Down Expand Up @@ -140,7 +138,7 @@ ANALYZE TABLE TableNameList [WITH NUM BUCKETS|TOPN|CMSKETCH DEPTH|CMSKETCH WIDTH

> **注意：**
>
> 该语法为全量收集。例如，在使用该语法收集了 a 列和 b 列的统计信息之后，如果还想要增加收集 c 列的统计信息，需要在语法中同时指定这三列 `ANALYZE table t columns a, b, c`，而不是只指定新增的那一列 `ANALYZE TABLE t COLUMNS c`。
> 该语法为全量收集。例如，在使用该语法收集了 a 列和 b 列的统计信息之后，如果还想要增加收集 c 列的统计信息，需要在语法中同时指定这三列 `ANALYZE TABLE t columns a, b, c`，而不是只指定新增的那一列 `ANALYZE TABLE t COLUMNS c`。

- 如果要收集 `PREDICATE COLUMNS` 的统计信息，请进行以下操作：

Expand Down