一个SQL语句问题，比较难

115300111

$sql="SELECT author, subject FROM pw_threads WHERE tid=$tid LIMIT 1";

$sql="SELECT content FROM pw_tmsgs WHERE tid=$tid LIMIT 1";

$sql="SELECT author, subject, content FROM pw_posts WHERE tid=$tid ORDER BY pid limit 0,20";

三句合成一句。有办法？

arcow

干嘛要合成一句呢？三句不是很好吗？

一棵白菜

select a.author, b.subject, b.content , c.author as cauthor, c.subject as bsubject, c.content as cccntent from pw_threads as a left join pw_tmsgs as b using($tid) left join pw_posts as c using($tid) ORDER BY pid limit 0,20


没测试...........

HonestQiao

原帖由 115300111 于 2007-3-29 14:32 发表
$sql="SELECT author, subject FROM pw_threads WHERE tid=$tid LIMIT 1";

$sql="SELECT content FROM pw_tmsgs WHERE tid=$tid LIMIT 1";

$sql="SELECT author, subject, content FROM pw_posts WHERE tid=$tid ORDER BY pid limit 0,20";

可以合成，但是下面的合成方法，只是从合成的角度来考虑的，并没有考虑效率的问题。

1. 读取出来的信息，是否有主键呢？我们假设为post_id
2. sql1、sql2合成，很好做：

1. $sql = "SELECT author, subject, content  FROM pw_threads WHERE tid=$tid LIMIT 1";

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3. 2和sql3合成

1. $sql = "SELECT author, subject, content  FROM pw_threads WHERE
   
2. post_id = ( SELECT post_id FROM pw_threads WHERE tid=$tid LIMIT 1 )
   
3. OR
   
4. post_id IN ( SELECT post_id FROM pw_posts WHERE tid=$tid ORDER BY pid limit 0,20 )
   
5. ORDER BY pid
   
6. ";

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115300111

这么说来。。。不合并为好。。。