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
- TableNameList
- TableName
AnalyzeTableStmt ::=
'ANALYZE' ( 'TABLE' ( TableNameList | TableName ( 'INDEX' IndexNameList | 'PARTITION' PartitionNameList ( 'INDEX' IndexNameList )? ) ) | 'INCREMENTAL' 'TABLE' TableName ( 'PARTITION' PartitionNameList )? 'INDEX' IndexNameList ) AnalyzeOptionListOpt
TableNameList ::=
TableName (',' TableName)*
TableName ::=
Identifier ( '.' Identifier )?
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。