我有一个论坛网站,帖子(宝石)和文件附件(gemdetail)以及帖子的回复(宝石),回复也可以有文件附件(gemdetail)。由于帖子和回复都存储在同一个表中,因此它会产生一个有趣的左连接,它选择所有具有相关回复和详细信息的帖子。
我想在混音(评级)中添加另一个表格,允许用户对每个帖子进行评分。然后,我希望能够在同一个查询中获得每个帖子的总评分。如何添加总和(评级),以便输出的每一行都有gemid的总和。我知道我需要一个sum子查询(派生表w / ad-hoc结果集),类似于找到的here,但它高于我的技能集。提前谢谢。
表结构如下
table: gems
gemid title replygemid
----- ----- ----------
220 map NULL
223 inhabitants NULL
403 reply to map 220
table: gemdetail
gemid filename
------ --------
220 uganda-map.jpg
220 mozambique-map.jpg
223 uganda-inhabitants.jpg
223 kenya-inhabitants.jpg
403 mona-lisa-x8.jpg
table: rating (to be added)
gemid rating
----- -------
220 1
220 5
223 3
403 -1
我当前(简化)的查询
SELECT g.gemid as ggemid, g.title as gtitle, gemdetail.filename as gfilename, r.filename as rfilename
FROM (SELECT gems.* FROM gems ) g
LEFT JOIN
(SELECT title, x.gemid, x.replygemid, x.userid, y.filename from gems x
LEFT JOIN gemdetail y ON x.gemid = y.gemid ) r ON g.gemid = r.replygemid
LEFT JOIN gemdetail ON g.gemid = gemdetail.gemid
结果可能如下所示
ggemid replygemid gtitle gfilename rfilename
------ ---------- ------ --------------------- ----------------
220 403 Map uganda-map.jpg mona-lisa-x8.jpg
220 403 Map mozambique-map.jpg mona-lisa-x8.jpg
223 NULL Inhabitants uganda-inhabitants.jpg NULL
223 NULL Inhabitants kenya-inhabitants.jpg NULL
223 NULL Inhabitants kenya-inhabitants.jpg NULL
答案 0 :(得分:1)
我认为这就是你想要的:
SELECT g.gemid as ggemid, g.title as gtitle, gemdetail.filename as gfilename, r.filename as rfilename, rt.sum_rating
FROM (SELECT gems.* FROM gems ) g
LEFT JOIN
(SELECT title, x.gemid, x.replygemid, x.userid, y.filename from gems x
LEFT JOIN gemdetail y ON x.gemid = y.gemid ) r ON g.gemid = r.replygemid
LEFT JOIN gemdetail ON g.gemid = gemdetail.gemid
LEFT JOIN (SELECT gemid, SUM(rating) as sum_rating from rating GROUP BY gemid) rt ON g.gemid = rt.gemid
答案 1 :(得分:1)
<强>查询强>:
SELECT g.gemid as ggemid, g2.gemid as replygemid,
g.title as gtitle, gd.filename as gfilename,
gd2.filename as rfilename, SUM(rating) as rating
FROM gems g
INNER JOIN gemdetail gd ON g.gemid = gd.gemid
INNER JOIN rating r ON g.gemid = r.gemid
LEFT OUTER JOIN gems g2 ON g.gemid = g2.replygemid
LEFT OUTER JOIN gemdetail gd2 ON g2.gemid = gd2.gemid
GROUP BY g.gemid, g2.gemid, g.title,
gd.filename, gd2.filename
<强> Results 强>:
| GGEMID | REPLYGEMID | GTITLE | GFILENAME | RFILENAME | RATING |
|--------|------------|--------------|------------------------|------------------|--------|
| 220 | 403 | map | mozambique-map.jpg | mona-lisa-x8.jpg | 6 |
| 220 | 403 | map | uganda-map.jpg | mona-lisa-x8.jpg | 6 |
| 223 | (null) | inhabitants | kenya-inhabitants.jpg | (null) | 3 |
| 223 | (null) | inhabitants | uganda-inhabitants.jpg | (null) | 3 |
| 403 | (null) | reply to map | mona-lisa-x8.jpg | (null) | -1 |