PHP MySQL 从两个表中选择数据并按第三个表中的字段排序

Question

请给我以下表格

Field
+----+--------+----------+---------------------+
| id | name   | Type     | date                |
+----+--------+----------+---------------------+
|  1 |  price | int      | 2009-09-02 00:07:07 |
|  2 |  width | float    | 2009-09-02 00:07:08 |
|  3 |  height| float    | 2009-09-02 00:07:30 |
+----+--------+--------------------------------+


Post
+----+--------+---------------------------------+
| id |title   | Body                            |
+----+--------+---------------------------------+
|  1 |  test  | Bla bla bla                     |
|  2 | Hello  | Bla bla bla                     |
|  3 | Its me | Bla bla bla                     | 
+----+--------+---------------------------------+


Post_Annex
+----+--------+----------+---------------------+
| id | IdPost | IdField  | Value               |
+----+--------+----------+---------------------+
|  1 |  1     | 1        | 50                  |
|  2 |  1     | 2        | 21                  |
|  3 |  1     | 3        | 3                   |
|  4 |  2     | 1        | 10                  |
|  5 |  2     | 2        | 2                   |
|  6 |  2     | 3        | 150                 |
|  7 |  3     | 1        | 1                   |
|  8 |  3     | 2        | 25                  |
|  9 |  3     | 3        | 15                  |
+----+--------+--------------------------------+

我希望从 Post 和 Post_Annex 表中选择数据，将它们按 Post 表的 Id 分组并按价格排序(这意味着通过 IdField当 Post_Annex 表等于 1 时)。所以这是我的查询:

SELECT p.title
    FROM Post p
    LEFT JOIN Post_Annex pa
       ON p.id = pa.IdPost

    GROUP BY p.id

    ORDER BY case when pa.IdField = 1 then 0 else 1, pa.Value DESC

这给了我这个顺序的结果:its Me |你好 |测试

这很好。但即使我尝试按宽度 (IdField = 2) 或高度 (IdField = 3) 排序，它也给了我相同的结果。

请高手有什么idea帮我解决这个问题？提前致谢。

Answer 1

我只想修改连接子句，指定要排序的字段:

SELECT p.title
FROM Post p
     LEFT JOIN Post_Annex pa
     ON p.id = pa.IdPost
        AND pa.idfield=1
ORDER BY pa.Value DESC

然后您就不必按 p.id 分组了。

您的查询并不总是有效，因为您按 p.id 分组，但您选择(并按其排序)其他非聚合列，并且这些列的值可以是 undetemined .