sql-statement-show-stats-histograms.md

title	summary	aliases
SHOW STATS_HISTOGRAMS	TiDB 数据库中 SHOW STATS_HISTOGRAMS 语句的简单说明。	/docs-cn/dev/sql-statements/sql-statement-show-histograms/ /zh/tidb/dev/sql-statement-show-histograms

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 ::=
    "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。

另请参阅

• ANALYZE
• 常规统计信息