Question

我有以下sql语句：

SELECT e.comment_id AS parentcomment,
m.comment_id AS child_id
FROM comments e
INNER JOIN comments m
ON e.comment_id=m.parent_id
WHERE e.parent='1' AND e.parent_id='$parentid' AND m.parent='0';

示例输出：

+---------------+----------+
| parentcomment | child_id |
+---------------+----------+
|             1 |        3 |
|             1 |        4 |
|             1 |        7 |
|             5 |        8 |
|             1 |        9 |
|             1 |       10 |
|             1 |       11 |
|             1 |       12 |
|             1 |       13 |
|             1 |       14 |
|             1 |       15 |
|             1 |       16 |
|             1 |       17 |
|             1 |       18 |
|             1 |       19 |
|             1 |       20 |
|             1 |       21 |
|             1 |       22 |
|             1 |       23 |
|             1 |       24 |
|             1 |       25 |
|            26 |       32 |
|            26 |       33 |
|            27 |       34 |
|            27 |       35 |
|            28 |       36 |
|            29 |       37 |
|            30 |       38 |
|            31 |       39 |
|            26 |       40 |
+---------------+----------+
30 rows in set

我想做什么 - 我只想为每个child_id值显示15个parentcomment值。除此之外，我只想要检索30个parentcomment值。

此外，我希望通过某个索引ORDER parentcomment值（让我们说id）并选出前30名，然后选出前15名有序的child_id值（也按id排序）。

希望这是有道理的。我该怎么办？

提前致谢。

Answer 1

你应该可以使用这个（sqlFiddle）这里我只抓取3（而不是15）child_id和6（而不是30）parentcomment

在我的示例中，$parentid为1。最里面的查询是您刚添加ORDER BY parentcomment,child_id

的原始查询

SELECT parentcomment,child_id,parentRank,childRank
FROM
    (SELECT parentcomment,
           child_id,
           IF (@prevparent <> parentcomment, @parentRank:=@parentRank+1, @parentRank) as parentRank,
           IF (@prevparent <> parentcomment, @childRank:=1, @childRank:=@childRank+1) as childRank,
           @prevparent := parentcomment
     FROM
       (SELECT e.comment_id AS parentcomment,
               m.comment_id AS child_id
        FROM comments e
        INNER JOIN comments m
        ON e.comment_id=m.parent_id
        WHERE e.parent='1' AND e.parent_id='1' AND m.parent='0'

          ORDER BY parentcomment,child_id
       )T1,
       (SELECT @prevparent:=0,@parentRank:=0,@childRank:=0)rank
     )T2
WHERE parentRank BETWEEN 1 AND 6
AND   childRank BETWEEN 1 AND 3

JOIN中特定列的ORDER / LIMIT

1 个答案: