MySQL JOIN和MAX

Question

您好我有一个查询，通过显示评价首先评论然后评论尚未评价的评论来做我想做的事情。但是我似乎无法正确订购。

结果如何：

5
4
0
0
...

目前正在这样做：

4
5
0
0
...

这是我的查询

$sql = $db->query( "
    SELECT branch.*, MAX(review.rating) AS m
    FROM branch
    LEFT OUTER JOIN review ON branch.bid = review.bid
    WHERE branch.address2 LIKE '$query' OR branch.postcode LIKE '$query-%'
    GROUP BY branch.bid
    ORDER BY m DESC, branch.branch ASC
    LIMIT $start,$limit 
" ) or die( "Select failed: (" . $db->errno . ") " . $db->error );

Answer 1

Meghraj Choudhary的子查询解决方案应该有效。

但是，加入更快。子查询需要额外的磁盘访问。假设branch.bid是主键，以下内容应该更快：

SELECT b1.*, b2.m FROM branch b1
INNER JOIN
(
SELECT branch.bid, MAX(review.rating) AS m
FROM branch
LEFT OUTER JOIN review ON branch.bid = review.bid
WHERE branch.address2 LIKE '$query' OR branch.postcode LIKE '$query-%'
GROUP BY branch.bid
LIMIT $start,$limit
) b2 ON
b1.bid = b2.bid
ORDER BY b2.m DESC, b1.branch ASC

我没试过这个。所以，请尝试并发回。