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我有以下表格
Children +--------------------------------------+ - Primary Key: childrenID (int) - Index: userID (int) - Index: childBirthDate (date) +--------------------------------------+ - childrenID - userID - childBirthDate - - 1 - 1 - 21/01/2000 - - 2 - 1 - 01/11/2013 - - 3 - 1 - 25/10/2013 - - 4 - 2 - 01/11/2013 - - 5 - 3 - 01/11/2013 - +--------------------------------------+ Users +------------------------+ - PRimary Key: userID (int) - Index: categoryGroup (vArchar) +------------------------+ - userID - categoryGroup - - 1 - 'Group1' - - 2 - 'Group1' - - 3 - 'Group2' - - 4 - 'Group2' - +------------------------+ CuponRequests +------------------------+ - Primary Key: ID (int) - Index: userID (int) - Index: cuponID (int) +-----------------------+ - ID - cuponID - userID - - 1 - 1 - 1 - - 1 - 2 - 1 - - 1 - 1 - 2 - +-----------------------+
这基本上是具有相关列的三个主要表
我有以下SQL查询来执行和获取我需要的结果.
SELECT users.userID,users.categoryGroup children.childBirthDate,children.childrenID From users,(SELECT * From (SELECT children.childrenID,children.childBirthDate,users.userID AS child_uid FROM children,users WHERE children.userID = users.userID ORDER BY children.childBirthDate DESC)t1 group by child_uid)children WHERE (children.childBirthDate <= DATE_Sub(CURDATE(),INTERVAL 5 MONTH)) AND (children.childBirthDate > DATE_SUB(CURDATE(),INTERVAL 6 MONTH)) AND (children.child_uid = users.userID) AND ('Group1,Group2' LIKE CONCAT('%',users.categoryGroup,'%')) AND NOT EXISTS (SELECT userID,cuponID FROM cuponRequests WHERE userID = users.userID AND cuponID = 1) AND userID = 1 ORDER BY children.childBirthDate DESC
对于此查询,我尝试仅在一个用户和一个优惠券上工作
但它的自然行为 – 查询正在对所有用户起作用
“cuponID”和间隔来自脚本的PHP端 – 我迭代“cupons”表(这里没有提到)并在每个“优惠券”行上执行此查询)
问题是此查询正在执行约1.5秒(O.O)
除了在CRON JOB环境中运行此脚本之外,此脚本也会在用户注册到网站后立即运行.我有96个杯子 – 这使得注册速度减慢了大约一分钟(这很多)
我想通了这个查询
SELECT * FROM (SELECT children.childrenID,users.userID AS child_uid FROM children,users WHERE children.userID = users.userID ORDER BY children.childBirthDate DESC)t1 GROUP BY child_uid
把事情放慢了.我尝试在选择查询中执行JOIN而不是选择查询,如下所示:
FROM users LEFT JOIN children ON children.userID = users.userID
但是后来我失去了“ORDER BY childBirthDate DESC”来获得这个用户最小的孩子,我失去了“GROUP BY child_uid”只让他的一个孩子
任何想法如何使事情更快但仍然有效?
P.S
抱歉我缺少英语.
编辑:
+----+--------------------+---------------+-------+----------------+---------+---------+------------------------------+-------+-----------------------------------------------------+ | id | select_tyPE | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+--------------------+---------------+-------+----------------+---------+---------+------------------------------+-------+-----------------------------------------------------+ | 1 | PRIMARY | NULL | NULL | NULL | NULL | NULL | NULL | NULL | Impossible WHERE noticed after reading const tables | | 4 | DEPENDENT SUBQUERY | cuponRequests | ref | userID,cuponID | userID | 5 | const | 1 | Using where | | 2 | DERIVED | <derived3> | ALL | NULL | NULL | NULL | NULL | 73526 | Using temporary; Using filesort | | 3 | DERIVED | users | index | PRIMARY | PRIMARY | 4 | NULL | 69271 | Using index; Using temporary; Using filesort | | 3 | DERIVED | children | ref | userID | userID | 4 | users.userID | 1 | | +----+--------------------+---------------+-------+----------------+---------+---------+------------------------------+-------+-----------------------------------------------------+
SELECT * FROM (SELECT children.childrenID,users WHERE children.userID = users.userID AND children.childBirthDate <= DATE_SUB(CURDATE(),INTERVAL 5 MONTH) AND children.childBirthDate > DATE_SUB(CURDATE(),INTERVAL 6 MONTH) ORDER BY children.childBirthDate DESC)t1 GROUP BY child_uid
编辑
我能写的最快的形式的完整查询.我已从LIKE中删除%,将子查询更改为连接并删除*.关于出生日期的条件也会被移动.但是可能会有错误.
SELECT users.userID,children.childrenID FROM (SELECT MIN(childBirthDate) AS childBirthDate,userID FROM children WHERE childBirthDate <= DATE_SUB(CURDATE(),INTERVAL 5 MONTH) AND childBirthDate > DATE_SUB(CURDATE(),INTERVAL 6 MONTH) GROUP BY userID) AS ch1 INNER JOIN users ON users.userID = ch1.userID INNER JOIN children ON users.userID = children.userID AND ch1.childBirthDate = children.childBirthDate LEFT JOIN CuponRequests ON CuponRequests.userID = userID AND cuponID = 1 WHERE ('Group1' LIKE users.categoryGroup OR 'Group2' LIKE users.categoryGroup) AND CuponRequest.ID IS NULL AND userID = 1 ORDER BY children.childBirthDate DESC
详细描述
>子查询可能很慢.有时优化器将无法做正确的事情.使用ON子句编写连接应该更安全.> GROUP BY的语句对于优化器来说更加复杂.在其中写入附加条件可能会有所帮助.>对LIKE’%something%’语句使用索引非常困难. LIKE’某事’%’或LIKE’某事’要快得多.>有时最好将*更改为所需参数的显式列表.有时所有需要的信息都在索引中,不需要直接从表中读取.在角落的情况下,它可能会有所帮助.
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