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:

ExplainSym

ExplainStmt:

ExplainStmt

ExplainableStmt:

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

EXPLAIN ANALYZE 是 MySQL 8.0 的功能,但该语句在 MySQL 中的输出格式和可能的执行计划都与 TiDB 有较大差异。

另请参阅

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