我有 MySQL 查询,当前选择并连接 13 个表,最后分组 ~60k 行。没有分组的查询需要 ~0ms,但有分组的查询时间增加到 ~1.7sec。用于分组的字段是主字段并被索引。问题出在哪里?
我知道没有聚合的分组被认为是无效查询和不良做法,但我需要不同的基表行并且不能使用 DISTINCT 语法。
查询本身如下所示:
SELECT `table_a`.*
FROM `table_a`
LEFT JOIN `table_b`
ON `table_b`.`invoice` = `table_a`.`id`
LEFT JOIN `table_c` AS `r1`
ON `r1`.`invoice_1` = `table_a`.`id`
LEFT JOIN `table_c` AS `r2`
ON `r2`.`invoice_2` = `table_a`.`id`
LEFT JOIN `table_a` AS `i1`
ON `i1`.`id` = `r1`.`invoice_2`
LEFT JOIN `table_a` AS `i2`
ON `i2`.`id` = `r2`.`invoice_1`
JOIN `table_d` AS `_u0`
ON `_u0`.`id` = 1
LEFT JOIN `table_e` AS `_ug0`
ON `_ug0`.`user` = `_u0`.`id`
JOIN `table_f` AS `_p0`
ON ( `_p0`.`enabled` = 1
AND ( ( `_p0`.`role` < 2
AND `_p0`.`who` IS NULL )
OR ( `_p0`.`role` = 2
AND ( `_p0`.`who` = '0'
OR `_p0`.`who` = `_u0`.`id` ) )
OR ( `_p0`.`role` = 3
AND ( `_p0`.`who` = '0'
OR `_p0`.`who` = `_ug0`.`group` ) ) ) )
AND ( `_p0`.`action` = '*'
OR `_p0`.`action` = 'read' )
AND ( `_p0`.`related_table` = '*'
OR `_p0`.`related_table` = 'table_name' )
JOIN `table_a` AS `_e0`
ON ( ( `_p0`.`related_id` = 0
OR `_p0`.`related_id` = `_e0`.`id`
OR `_p0`.`related_user` = `_e0`.`user`
OR `_p0`.`related_group` = `_e0`.`group` )
OR ( `_p0`.`role` = 0
AND `_e0`.`user` = `_u0`.`id` )
OR ( `_p0`.`role` = 1
AND `_e0`.`group` = `_ug0`.`group` ) )
AND `_e0`.`id` = `table_a`.`id`
JOIN `table_d` AS `_u1`
ON `_u1`.`id` = 1
LEFT JOIN `table_e` AS `_ug1`
ON `_ug1`.`user` = `_u1`.`id`
JOIN `table_f` AS `_p1`
ON ( `_p1`.`enabled` = 1
AND ( ( `_p1`.`role` < 2
AND `_p1`.`who` IS NULL )
OR ( `_p1`.`role` = 2
AND ( `_p1`.`who` = '0'
OR `_p1`.`who` = `_u1`.`id` ) )
OR ( `_p1`.`role` = 3
AND ( `_p1`.`who` = '0'
OR `_p1`.`who` = `_ug1`.`group` ) ) ) )
AND ( `_p1`.`action` = '*'
OR `_p1`.`action` = 'read' )
AND ( `_p1`.`related_table` = '*'
OR `_p1`.`related_table` = 'table_name' )
JOIN `table_g` AS `_e1`
ON ( ( `_p1`.`related_id` = 0
OR `_p1`.`related_id` = `_e1`.`id`
OR `_p1`.`related_user` = `_e1`.`user`
OR `_p1`.`related_group` = `_e1`.`group` )
OR ( `_p1`.`role` = 0
AND `_e1`.`user` = `_u1`.`id` )
OR ( `_p1`.`role` = 1
AND `_e1`.`group` = `_ug1`.`group` ) )
AND `_e1`.`id` = `table_a`.`company`
WHERE `table_a`.`date_deleted` IS NULL
AND `table_a`.`company` = 4
AND `table_a`.`type` = 1
AND `table_a`.`date_composed` >= '2016-05-04 14:43:55'
GROUP BY `table_a`.`id`
最佳答案
OR
会降低性能。
这个复合索引可能会有所帮助:INDEX(company, type, date_deleted, date_composed)
。
LEFT JOIN table_b ON table_b.invoice = table_a.id
似乎除了减慢处理速度之外什么也没做。 table_b
的字段未被使用或SELECTed
。由于它是 LEFT
连接,因此不限制输出。等等。如果它被删除,或者证明它是正确的。
其他连接也是如此。
JOIN
和GROUP BY
会发生什么:首先,执行所有连接;这会激增中间“表”中的行数。然后 GROUP BY
内爆行集。
避免这种爆炸-内爆缓慢的一种技术是做
SELECT ...,
( SELECT ... ) AS ...,
...
而不是 JOIN
或 LEFT JOIN
。但是,这仅在子查询中有零行或一行时才有效。通常,当可以将聚合(例如 SUM
)移动到子查询中时,这很有用。
如需进一步讨论,请包含SHOW CREATE TABLE
。
关于MySQL group by 会破坏查询性能,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/37652938/