文档目录

ANALYZE TABLE

ANALYZE TABLE 语句用于更新 TiDB 在表和索引上留下的统计信息。执行大批量更新或导入记录后,或查询执行计划不是最佳时,建议运行 ANALYZE TABLE

当 TiDB 逐渐发现这些统计数据与预估不一致时,也会自动更新其统计数据。

语法图

AnalyzeTableStmt:

AnalyzeTableStmt

TableNameList:

TableNameList

TableName:

TableName

示例

mysql> CREATE TABLE t1 (id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, c1 INT NOT NULL);
Query OK, 0 rows affected (0.11 sec)

mysql> INSERT INTO t1 (c1) VALUES (1),(2),(3),(4),(5);
Query OK, 5 rows affected (0.03 sec)
Records: 5  Duplicates: 0  Warnings: 0

mysql> ALTER TABLE t1 ADD INDEX (c1);
Query OK, 0 rows affected (0.30 sec)

mysql> EXPLAIN SELECT * FROM t1 WHERE c1 = 3;
+-------------------+-------+------+-----------------------------------------------------------------+
| id                | count | task | operator info                                                   |
+-------------------+-------+------+-----------------------------------------------------------------+
| IndexReader_6     | 10.00 | root | index:IndexScan_5                                               |
| └─IndexScan_5     | 10.00 | cop  | table:t1, index:c1, range:[3,3], keep order:false, stats:pseudo |
+-------------------+-------+------+-----------------------------------------------------------------+
2 rows in set (0.00 sec)

mysql> analyze table t1;
Query OK, 0 rows affected (0.13 sec)

mysql> EXPLAIN SELECT * FROM t1 WHERE c1 = 3;
+-------------------+-------+------+---------------------------------------------------+
| id                | count | task | operator info                                     |
+-------------------+-------+------+---------------------------------------------------+
| IndexReader_6     | 1.00  | root | index:IndexScan_5                                 |
| └─IndexScan_5     | 1.00  | cop  | table:t1, index:c1, range:[3,3], keep order:false |
+-------------------+-------+------+---------------------------------------------------+
2 rows in set (0.00 sec)

MySQL 兼容性

ANALYZE TABLE 在语法上与 MySQL 类似。但 ANALYZE TABLE 在 TiDB 上执行所需时间可能长得多,因为它的内部运行方式不同。

另请参阅