explain-analyze.md

title	summary	category
EXPLAIN ANALYZE	TiDB 数据库中 EXPLAIN ANALYZE 的使用概况。	reference

EXPLAIN ANALYZE

EXPLAIN ANALYZE 语句的工作方式类似于 EXPLAIN，主要区别在于前者实际上会执行语句。这样可以将查询计划中的估计值与执行时所遇到的实际值进行比较。如果估计值与实际值显著不同，那么应考虑在受影响的表上运行 ANALYZE TABLE。

语法图

ExplainSym:

ExplainStmt:

ExplainableStmt:

示例

mysql> CREATE TABLE t1 (id INT NOT NULL PRIMARY KEY auto_increment, c1 INT NOT NULL);
Query OK, 0 rows affected (0.12 sec)

mysql> INSERT INTO t1 (c1) VALUES (1), (2), (3);
Query OK, 3 rows affected (0.02 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> EXPLAIN ANALYZE SELECT * FROM t1 WHERE id = 1;
+-------------+-------+------+--------------------+---------------------------+
| id          | count | task | operator info      | execution info            |
+-------------+-------+------+--------------------+---------------------------+
| Point_Get_1 | 1.00  | root | table:t1, handle:1 | time:0ns, loops:0, rows:0 |
+-------------+-------+------+--------------------+---------------------------+
1 row in set (0.01 sec)

mysql> EXPLAIN ANALYZE SELECT * FROM t1;
+-------------------+----------+------+-------------------------------------------------------------+----------------------------------+
| id                | count    | task | operator info                                               | execution info                   |
+-------------------+----------+------+-------------------------------------------------------------+----------------------------------+
| TableReader_5     | 10000.00 | root | data:TableScan_4                                            | time:931.759µs, loops:2, rows:3  |
| └─TableScan_4     | 10000.00 | cop  | table:t1, range:[-inf,+inf], keep order:false, stats:pseudo | time:0s, loops:0, rows:3         |
+-------------------+----------+------+-------------------------------------------------------------+----------------------------------+
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

• Understanding the Query Execution Plan
• EXPLAIN
• ANALYZE TABLE
• TRACE