MySQL 旋转行和列

Question

我有一个包含一些用户数据的表，第二个包含用户属性数据的表。这些属性总是 2，而且我知道它们的名字。我需要一个查询来检索单个结构中的所有内容。但是，我无法更改数据库架构。

这是我的数据库的简化版本:

用户

+-------------------+--------------+------+-----+---------+-------+
| Field             | Type         | Null | Key | Default | Extra |
+-------------------+--------------+------+-----+---------+-------+
| username          | varchar(64)  | NO   | PRI | NULL    |       |
| name              | varchar(100) | YES  |     | NULL    |       |
+-------------------+--------------+------+-----+---------+-------+

用户属性

+-----------+--------------+------+-----+---------+-------+
| Field     | Type         | Null | Key | Default | Extra |
+-----------+--------------+------+-----+---------+-------+
| username  | varchar(64)  | NO   | PRI | NULL    |       |
| propName  | varchar(100) | NO   | PRI | NULL    |       |
| propValue | text         | NO   |     | NULL    |       |
+-----------+--------------+------+-----+---------+-------+

因此，例如，有以下数据:

用户

username         name
1                User1
2                User2

用户属性

username         propName         propValue
1                status           "At work"
1                picture          "pict1.jpg"
2                status           "Busy"
2                picture          "pict2.jpg"

我需要以下结果:

username         name             STATUS          PICTURE
1                User1            "At work"       "pict1.jpg"
2                User2            "Busy"          "pict2.jpg"

我在互联网上做了一些研究，显然这是通过PIVOT实现的，但MySQL不包含此功能。按照此处的答案:MySQL pivot table ，我可以设法得到这个:

select ou.username, 
    case when (oup.propName='status') then oup.propValue end as 'STATUS',
    case when (oup.propName='picture') then oup.propValue end as 'PICTURE'
from User ou, User_Properties oup
where ou.username = oup.username;

username         name             STATUS          PICTURE
1                User1            "At work"       null
1                User1            null            "pict1.jpg"
2                User2            "Busy"          null
2                User2            null            "pict2.jpg"

结果分为两行。如果我按用户名对结果进行分组，我得到的图片数据始终为空:

select ou.username, 
    case when (oup.propName='status') then oup.propValue end as 'STATUS',
    case when (oup.propName='picture') then oup.propValue end as 'PICTURE'
from User ou, User_Properties oup
where ou.username = oup.username
group by oup.username;

username         name             STATUS          PICTURE
1                User1            "At work"       null
2                User2            "Busy"          null

我错过了什么？谢谢。

编辑:https://stackoverflow.com/users/1529673/strawberry给出了解决方案:

select ou.username, 
    MAX(case when (oup.propName='status') then oup.propValue end) as 'STATUS',
    MAX(case when (oup.propName='picture') then oup.propValue end) as 'PICTURE'
from User ou, User_Properties oup
where ou.username = oup.username;

Answer 1

https://stackoverflow.com/users/1529673/strawberry给出了解决方案:

select ou.username, 
    MAX(case when oup.propName='status' then oup.propValue end) as 'STATUS',
    MAX(case when oup.propName='picture' then oup.propValue end) as 'PICTURE'
from User ou
Join User_Properties oup
On ou.username = oup.username;