Question

我有两张桌子：宝石和宝石都留下了。我试图将LEFT JOIN限制为gems表中的10条记录。还有另外两个表加入（gemreply和用户），但它们没有解决问题。以下不起作用：

SELECT gems.gemid, gems.title, r.tot, gemdetail.filename FROM ((gems 
LEFT JOIN (SELECT gemid, COUNT(*) AS tot FROM gemreply GROUP BY gemid) AS r ON gems.gemid = r.gemid) 
LEFT JOIN gemdetail ON gems.gemid = gemdetail.gemid) 
LEFT JOIN users ON gems.userid = users.userid 
WHERE gems.grade = '7' ORDER BY gems.gemid LIMIT 0, 10;

这会将返回的行总数限制为10，但由于每个gem都有多个详细记录，因此我只剩下少于10个gem记录。我已阅读每篇“LIMIT”帖子，但未发现这种情况。

更新1：好的 - 感谢jviladrich - 它奏效了。这是代码：

SELECT gems.gemid, gems.title, r.tot, gemdetail.filename  
FROM ((gems 
INNER JOIN (SELECT gems.gemid from gems WHERE gems.grade = '7'  ORDER BY gems.gemid LIMIT 0, 10) g
ON (gems.gemid = g.gemid)
LEFT JOIN (SELECT gemid, COUNT(*) AS tot FROM gemreply GROUP BY gemid) AS r ON gems.gemid = r.gemid) 
LEFT JOIN gemdetail ON gems.gemid = gemdetail.gemid) 
LEFT JOIN users ON gems.userid = users.userid ;

更新2：下面yogeshr的代码也可以运行 - 可能就是我要使用的代码。谢谢你们两位！

Answer 1

像这样的东西

   SELECT * FROM A
      INNER JOIN ( SELECT * FROM A WHERE A.FIELD1='X' ORDER BY A.FIELD2 LIMIT 10) X
             ON (A.KEYFIELD=X.KEYFIELD)
      LEFT JOIN B ON (A.FIELD = B.FIELD)
      LEFT JOIN C ON (A.FIELD = C.FIELD)

Answer 2

试试这个：

SELECT g.gemid, g.title, r.tot, gemdetail.filename
FROM (SELECT * FROM gems WHERE grade = '7' LIMIT 10) g
LEFT JOIN (SELECT gemid, COUNT(*) AS tot FROM gemreply GROUP BY gemid) r
          ON r.gemid = g.gemid
LEFT JOIN gemdetail ON g.gemid = gemdetail.gemid
LEFT JOIN users ON g.userid = users.userid
ORDER BY g.gemid;

这应该有用。

在第一个表上限制左连接

2 个答案: