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我什至不确定标题是否正确，但这是简化的情况。

我有一张表，其中包含邻接列表：

comments
- id (int)
- parent_id (int)
- depth_level (int)
- ...

我想要做的是用 order by 和 limit 查询深度级别 0，对于返回的每一行我想要一个联合查询，该查询返回相同的表和 order by 和 limit 但不同的深度级别，我想要那个子查询只返回与父深度级别相关的行......等等。如果有帮助，我可以限制深度级别。我有点没有参考，像这样：

select * from ( select * from comments where depth = 0 order by id asc LIMIT 10 ) D0
union all 
select * from ( select * from comments where depth = 1 order by id asc LIMIT 10 ) D1

我得到联合行，但正如你所看到的，我希望 D1 只包含具有 parent_id 和 D0 id 的行......我希望它用于多个级别。也许这是错误的方法。我知道这是一厢情愿的想法，但如果行数超过提供的限制，如果我能以某种方式获得每一行，那就太好了。

一个例子：

id  parent_id   depth   title
1   0           0       Title 1
2   0           0       Title 2
3   1           1       Title 3
4   1           1       Title 4
5   1           1       Title 5
6   1           1       Title 6
7   1           1       Title 7
8   4           2       Title 8
9   4           2       Title 9
10  4           2       Title 10
11  4           2       Title 11

pseudo:
select * from table where depth = 0 order by id asc limit 1
union 
select * from table where depth = 1 and parent_id from firstQuery.id order by id asc limit 2
union
select * from table where depth = 2 and parent_id from secondQuery.id order by id asc limit 3

result:

id  parent_id   depth   title
1   0           0       Title 1
3   1           1       Title 3
4   1           1       Title 4
8   4           2       Title 8
9   4           2       Title 9
10  4           2       Title 10

编辑2：

扩展彼得姆的答案。

(
SELECT *
FROM comments
WHERE depth = 0
ORDER BY id DESC
LIMIT 2
)
UNION ALL
(
  SELECT c.*
    FROM comments c JOIN 
    (
      SELECT id
      FROM comments
      WHERE depth = 0
      ORDER BY id DESC
      LIMIT 2
    ) p ON c.parent_id = p.id
    LIMIT 5
)


id  parent_id   depth   title
1   0           0       Title 1
2   0           0       Title 2
3   1           1       Title 3
4   1           1       Title 4
5   1           1       Title 5
6   1           1       Title 6
7   1           1       Title 7

但我想要的是限制每个父深度级别，而不是限制深度级别的总和。像这样（在这个例子中，每个深度 1 5 个）：

id  parent_id   depth   title
1   0           0       Title 1
2   0           0       Title 2
3   1           1       Title 3
4   1           1       Title 4
5   1           1       Title 5
6   1           1       Title 6
7   1           1       Title 7
8   2           1       Title 8
9   2           1       Title 9
10  2           1       Title 10
11  2           1       Title 11
12  2           1       Title 12
4

1 回答 1

1

这很难看，但你可以做到

(
  SELECT *
   FROM comments
  WHERE depth = 0
  ORDER BY id
  LIMIT 1
)
UNION ALL
(
  SELECT c.*
   FROM comments c JOIN 
  (
    SELECT id
     FROM comments
    WHERE depth = 0
    ORDER BY id
    LIMIT 1
  ) p ON c.parent_id = p.id
   LIMIT 2
)
UNION ALL
(
  SELECT c.*
   FROM comments c JOIN 
  (
    SELECT c.*
     FROM comments c JOIN 
    (
      SELECT id
       FROM comments
      WHERE depth = 0
      ORDER BY id
      LIMIT 1
    ) q ON c.parent_id = q.id
     LIMIT 2
  ) p ON c.parent_id = p.id
   LIMIT 3
)
-- ORDER BY id

输出：

| 身份证 | 父 ID | 深度 | 标题 |
|----|------------|--------|----------|
| 1 | 0 | 0 | 标题 1 |
| 3 | 1 | 1 | 标题 3 |
| 4 | 1 | 1 | 标题 4 |
| 8 | 4 | 2 | 标题 8 |
| 9 | 4 | 2 | 标题 9 |
| 10 | 4 | 2 | 标题 10 |

这是SQLFiddle演示

于 2013-10-01T00:53:50.480 回答