- 求助MySQL的关于sql语句怎么写？？三表的查询~~~请大神进来帮忙~~~~~
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现在我有三个表：
表1：
pre_common_member_profile：
uid（用户的uid）,
gender（性别）,
birthyear（出生的年），
birthmonth（出生的月）,
birthday（出生的日）
表2：
pre_home_friend：
uid（用户的uid），
fuid（加为好友的uid）
表3：
pre_home_friend_request：
fuid(发送好友请求的人)，
uid(发送给谁)要求：
查找表1，但是排除一定条件。查询表1上面的五个字段，条件为uid=570并且uid不能等于（这两个条件：1、表2中uid=570的fuid的值。2、表3中的fuid=570的uid值。）
请尽量写出的语句效率高一点。
@bdmh
select gender,uid,birthmonth,birthday,birthyear from pre_common_member_profile as p where destination = '济南' and p.uid <> 570 and p.uid < 570 and gender = 0 and uid not in(select fuid from pre_home_friend where uid=570 union select uid from pre_home_friend_request where fuid = 570) order by uid desc
怎么优化一下？？
select * from 表1 t1 where t1.uid = 570
and uid not in
(select fuid from 表2 where uid = 570
union
select uid from 表3 where fuid = 570);
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- elainetian3 select gender,uid,birthmonth,birthday,birthyear from pre_common_member_profile as p where destination = '济南' and p.uid <> 570 and p.uid < 570 and gender = 0 and uid not in(select fuid from pre_home_friend where uid=570 union select uid from pre_home_friend_request where fuid = 570) order by uid desc 怎么优化一下？？
- 接近 4 年之前 回复
select A.id,B.id,C.id from A inner join B on A.id=B.id inner join C on C.id=A.id
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- elainetian3 select gender,uid,birthmonth,birthday,birthyear from pre_common_member_profile as p where destination = '济南' and p.uid <> 570 and p.uid < 570 and gender = 0 and uid not in(select fuid from pre_home_friend where uid=570 union select uid from pre_home_friend_request where fuid = 570) order by uid desc 怎么优化一下？？
- 接近 4 年之前 回复
直接select gender,uid,birthmonth,birthday,birthyear from pre_common_member_profile as p where destination = '济南' and p.uid < 570 and gender = 0 order by uid desc
uid not in(select fuid from pre_home_friend where uid=570 union select uid from pre_home_friend_request where fuid = 570) 这个没必要，这个始终取得的是空
uid<>570 ,你uid<570 了，还会等于570吗？
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- elainetian3 还有可能有大于570的 我这句是想排除它本身
- 接近 4 年之前 回复
这个SQL不难写，给你分析下SQL的优化
pre_home_friend 的 uid字段建立索引
pre_home_friend_request 的 fuid建立索引
pre_common_member_profile 的uid是主键的话，应该是有索引的。修改UID的索引的排序方式为 desc ，默认是ASC的，你可以看下
使用NOT EXISTS 替换not in；
然后看SQL的执行计划。看索引有没有生效
select A.id,B.id,C.id from A inner join B on A.id=B.id inner join C on C.id=A.id
select A from B
sellect *
