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_index0 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_countNULL 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 allEvictedallLoaded
Total_mem_usage总内存占用
Hist_mem_usage历史内存占用
Topn_mem_usageTopN 内存占用
Cms_mem_usageCMS 内存占用

语法图

ShowStatsHistogramsStmt
SHOWSTATS_HISTOGRAMSShowLikeOrWhere
ShowLikeOrWhere
LIKESimpleExprWHEREExpression

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

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