SHOW STATS_HISTOGRAMS
此语句显示由 ANALYZE
语句 作为数据库 统计信息 一部分收集的直方图信息。
目前,SHOW STATS_HISTOGRAMS
语句返回以下列:
列名 | 描述 |
---|---|
Db_name | 数据库名称 |
Table_name | 表名 |
Partition_name | 分区名称 |
Column_name | 列名(当 is_index 为 0 时)或索引名(当 is_index 为 1 时) |
Is_index | 是否为索引列 |
Update_time | 更新时间 |
Distinct_count | 不同值数量 |
Null_count | NULL 值数量 |
Avg_col_size | 列的平均大小 |
Correlation | 该列与整数主键列之间的 Pearson 相关系数,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 | 总内存使用量 |
Hist_mem_usage | 历史内存使用量 |
Topn_mem_usage | TopN 内存使用量 |
Cms_mem_usage | CMS 内存使用量 |
概要
- 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 行结果(0.00 秒)
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 行结果(0.00 秒)
MySQL 兼容性
此语句是 TiDB 对 MySQL 语法的扩展。