SHOW STATS_HISTOGRAMS
你可以使用 SHOW STATS_HISTOGRAMS 语句查看通过 ANALYZE 语句收集的直方图信息，该内容是数据库常规统计信息的一部分。
目前，SHOW STATS_HISTOGRAMS 语句返回以下列：
| 列名 | 说明 |
|---|---|
Db_name | 数据库名 |
Table_name | 表名 |
Partition_name | 分区名 |
Column_name | 取决于 Is_index 值：Is_index 为 0 时显示列名，为 1 时显示索引名 |
Is_index | 是否是索引列 |
Update_time | 更新时间 |
Distinct_count | 不同值数量 |
Null_count | NULL 的数量 |
Avg_col_size | 列平均长度 |
Correlation | 该列与整型主键的皮尔逊系数，表示两列之间的关联程度 |
Load_status | 加载状态，例如 allEvicted 和 allLoaded |
Total_mem_usage | 总内存占用 |
Hist_mem_usage | 历史内存占用 |
Topn_mem_usage | TopN 内存占用 |
Cms_mem_usage | CMS 内存占用 |
语法图
- ShowStatsHistogramsStmt
- ShowLikeOrWhere
ShowStatsHistogramsStmt ::=
"SHOW" "STATS_HISTOGRAMS" ShowLikeOrWhere?
ShowLikeOrWhere ::=
"LIKE" SimpleExpr
| "WHERE" Expression
示例
SHOW STATS_HISTOGRAMS;
+---------+------------+----------------+-------------+----------+---------------------+----------------+------------+--------------+-------------+
| Db_name | Table_name | Partition_name | Column_name | Is_index | Update_time | Distinct_count | Null_count | Avg_col_size | Correlation |
+---------+------------+----------------+-------------+----------+---------------------+----------------+------------+--------------+-------------+
| test | t | | a | 0 | 2020-05-25 19:20:00 | 7 | 0 | 1 | 1 |
| test | t2 | | a | 0 | 2020-05-25 19:20:01 | 6 | 0 | 8 | 0 |
| test | t2 | | b | 0 | 2020-05-25 19:20:01 | 6 | 0 | 1.67 | 1 |
+---------+------------+----------------+-------------+----------+---------------------+----------------+------------+--------------+-------------+
3 rows in set (0.00 sec)
SHOW STATS_HISTOGRAMS WHERE table_name = 't2';
+---------+------------+----------------+-------------+----------+---------------------+----------------+------------+--------------+-------------+
| Db_name | Table_name | Partition_name | Column_name | Is_index | Update_time | Distinct_count | Null_count | Avg_col_size | Correlation |
+---------+------------+----------------+-------------+----------+---------------------+----------------+------------+--------------+-------------+
| test | t2 | | b | 0 | 2020-05-25 19:20:01 | 6 | 0 | 1.67 | 1 |
| test | t2 | | a | 0 | 2020-05-25 19:20:01 | 6 | 0 | 8 | 0 |
+---------+------------+----------------+-------------+----------+---------------------+----------------+------------+--------------+-------------+
2 rows in set (0.00 sec)
MySQL 兼容性
该语句是 TiDB 对 MySQL 语法的扩展。