Question

我有2个表 - 帖子和元

帖子结构：

+---------+---------+
|   id    |  title  |
+---------+---------+

元结构：

+---------+---------+---------+
|   post  |   key   |  value  |
+---------+---------+---------+

我需要选择meta.key为“end”或“result”的记录，并通过post.id选择goup（如果有“end”和“result”元键的话）

这是我的尝试：

SELECT
posts.id,
posts.title,
meta.post,
meta.`value`,
CASE meta.`key` WHEN 'result' THEN value END AS 'result',
CASE meta.`key` WHEN 'end' THEN value END AS 'end'
FROM
posts
INNER JOIN meta ON posts.id = meta.post
WHERE meta.`key` IN ('result', 'end')

它返回两个单独的记录，一个是meta.key“end”，另一个是“result”。

+------------+------------+------------+------------+------------+------------+
|    id      |   title    |   post     |   value    |   result   |     end    |
+------------+------------+------------+------------+------------+------------+
|     1      |  Untitled  |      1     |     5      |    (Null)  | 1344240000 |
+------------+------------+------------+------------+------------+------------+
|     1      |  Untitled  |      1     |   88:79    |    88:79   |   (Null)   |
+------------+------------+------------+------------+------------+------------+

我需要的是将这两个记录合并为一个：

+------------+------------+------------+------------+------------+------------+
|    id      |   title    |   post     |   value    |   result   |     end    |
+------------+------------+------------+------------+------------+------------+
|     1      |  Untitled  |      1     |     -      |    88:79   | 1344240000 |
+------------+------------+------------+------------+------------+------------+

Answer 1

你可以通过两次INNER JOINing meta来做到这一点，即

SELECT

  p.id,
  p.title,
  mr.value AS result,
  me.value AS end

FROM posts AS p

INNER JOIN meta AS mr

  ON mr.post = p.id
  AND mr.`key` = 'result'

INNER JOIN meta AS me
  ON me.post = p.id
  AND me.`key` = 'end';

SQL小提琴链接：http://sqlfiddle.com/#!2/2a89e/5

Answer 2

由于您尝试 pivot 数据，因此通常会使用CASE的聚合函数：

SELECT
  posts.id,
  posts.title,
  -- meta.post,
  -- meta.`value`,
  max(CASE meta.`key` WHEN 'result' THEN value END) AS 'result',
  max(CASE meta.`key` WHEN 'end' THEN value END) AS 'end'
FROM posts
INNER JOIN meta 
  ON posts.id = meta.post
WHERE meta.`key` IN ('result', 'end')
GROUP BY posts.id, posts.title  -- , meta.post, meta.`value`

请参阅SQL Fiddle with Demo

注意：您为value列显示了两个单独的值，您需要决定选择值的逻辑，因为如果执行group by时它们是不同的，您将获得多行。因此，您会看到我已注释掉这两列，因为它们已在CASE中使用，并且已显示post列。

Answer 3

只要“结果”只有一行，每个帖子ID只有一行“结束”，您可以使用MAX作为原始查询的聚合函数，最后使用posts.id进行分组;我无法弄明白你VALUE的逻辑，所以我暂时把它遗弃了;

SELECT posts.id, posts.title,
  MAX(CASE meta.`key` WHEN 'result' THEN value END) AS 'result',
  MAX(CASE meta.`key` WHEN 'end' THEN value END)  AS 'end'
FROM posts
INNER JOIN meta ON posts.id = meta.post
WHERE meta.`key` IN ('result', 'end')
GROUP BY posts.id, posts.title

An SQLfiddle to test with

按行的值分隔一列到两列

3 个答案: