慢查询优化案例之将子查询替换为临时表再与其他表进行表关联
一 问题描述
有个这样的慢查询，执行需要1.8秒，且该慢查询在另一个慢查询中被调用了几十次，执行长达200秒：
SELECT
ce.orgCode,
ce.serialNum
FROM
clue ce
LEFT JOIN clue pce ON pce.serialNum = ce.parentId
LEFT JOIN (
SELECT
ni.nodeCode,
IF (
ni.workActivityID IS NULL,
ce.statusDate,
ni.opreateDate
) AS 'statusDate'
FROM
nodeInfo ni
LEFT JOIN clue ce ON ni.nodeCode = ce.serialNum
WHERE
(
ni.workActivityID = 'finish_clue'
AND ni.nextOperation = '00'
OR (
(
ni.workActivityID = 'four_approve_2'
AND ni.nextOperation = '4'
)
OR (
ni.workActivityID = 'three_approve_2'
AND ni.nextOperation = '4'
)
)
OR ce. STATUS IN (
'251',
'252',
'253',
'254',
'255',
'219B'
)
)
AND ni.nodeCode LIKE 'XS-%'
GROUP BY
ni.nodeCode
) cezt ON cezt.nodeCode = ce.serialNum执行计划如下：
查看下该表的索引：
发现group by没有走ni的索引nodeInfo_nodeCode。
强制走这个索引后，查询也还是很慢，1.8秒：
单独执行cezt里的这个sql：
SELECT
ni.nodeCode,
IF (
ni.workActivityID IS NULL,
ce.statusDate,
ni.opreateDate
) AS 'statusDate'
FROM
nodeInfo ni
LEFT JOIN clue ce ON ni.nodeCode = ce.serialNum
WHERE
(
ni.workActivityID = 'finish_clue'
AND ni.nextOperation = '00'
OR (
(
ni.workActivityID = 'four_approve_2'
AND ni.nextOperation = '4'
)
OR (
ni.workActivityID = 'three_approve_2'
AND ni.nextOperation = '4'
)
)
OR ce. STATUS IN (
'251',
'252',
'253',
'254',
'255',
'219B'
)
)
AND ni.nodeCode LIKE 'XS-%'
GROUP BY ni.nodeCode
也不算慢，0.1秒，也是全表扫描的ni，返回1万行数据。
二 优化思路
把这个包含group by的子查询插入到一个临时表里，再和外面的表进行关联
2.1 把以下sql的查询结果放入一个临时表里
示例：
CREATE TABLE baidd_test_20200803 AS
SELECT
ni.nodeCode,
IF (
ni.workActivityID IS NULL,
ce.statusDate,
ni.opreateDate
) AS 'statusDate'
FROM
nodeInfo ni
LEFT JOIN clue ce ON ni.nodeCode = ce.serialNum
WHERE
(
ni.workActivityID = 'finish_clue'
AND ni.nextOperation = '00'
OR (
(
ni.workActivityID = 'four_approve_2'
AND ni.nextOperation = '4'
)
OR (
ni.workActivityID = 'three_approve_2'
AND ni.nextOperation = '4'
)
)
OR ce. STATUS IN (
'251',
'252',
'253',
'254',
'255',
'219B'
)
)
AND ni.nodeCode LIKE 'XS-%'
GROUP BY
ni.nodeCode
2.2 在该临时表的nodeCode上创建一个索引
CREATE INDEX ind_tmp_nodeCode ON baidd_test_20200803(nodeCode);
2.3 改写sql
将所有以下sql：
(
SELECT
ni.nodeCode,
IF (
ni.workActivityID IS NULL,
ce.statusDate,
ni.opreateDate
) AS 'statusDate'
FROM
nodeInfo ni
LEFT JOIN clue ce ON ni.nodeCode = ce.serialNum
WHERE
(
ni.workActivityID = 'finish_clue'
AND ni.nextOperation = '00'
OR (
(
ni.workActivityID = 'four_approve_2'
AND ni.nextOperation = '4'
)
OR (
ni.workActivityID = 'three_approve_2'
AND ni.nextOperation = '4'
)
)
OR ce. STATUS IN (
'251',
'252',
'253',
'254',
'255',
'219B'
)
)
AND ni.nodeCode LIKE 'XS-%'
GROUP BY ni.nodeCode
)替换为baidd_test_20200803
2.4 示例
修改前的sql：
SELECT
ce.orgCode,
ce.serialNum
FROM
clue ce
LEFT JOIN clue pce ON pce.serialNum = ce.parentId
LEFT JOIN (
SELECT
ni.nodeCode,
IF (
ni.workActivityID IS NULL,
ce.statusDate,
ni.opreateDate
) AS 'statusDate'
FROM
nodeInfo ni
LEFT JOIN clue ce ON ni.nodeCode = ce.serialNum
WHERE
(
ni.workActivityID = 'finish_clue'
AND ni.nextOperation = '00'
OR (
(
ni.workActivityID = 'four_approve_2'
AND ni.nextOperation = '4'
)
OR (
ni.workActivityID = 'three_approve_2'
AND ni.nextOperation = '4'
)
)
OR ce. STATUS IN (
'251',
'252',
'253',
'254',
'255',
'219B'
)
)
AND ni.nodeCode LIKE 'XS-%'
GROUP BY ni.nodeCode
) cezt ON cezt.nodeCode = ce.serialNum
修改后的sql：
SELECT
ce.orgCode,
ce.serialNum
FROM
clue ce
LEFT JOIN clue pce ON pce.serialNum = ce.parentId
LEFT JOIN baidd_test_20200803 cezt ON cezt.nodeCode = ce.serialNum查询结果由1.8秒降为0.02秒。