Question

我有一个名为'computers'的表，其中包含以下cols：
ROW_ID
COMPUTER_ID
关键
值

键等于'3'的行的值包含计算机的名称 key等于'4'的行的值包含计算机的IP 键等于'5'的行的值包含计算机的用户
Computer_id代表一个特定的唯一计算机
我想创建一个具有以下列的视图：
COMPUTER_ID
命名
IP_ADDRESS
用户

我正在努力解决这个问题。我确信它不会那么复杂，但很难尝试多次引用相同的列（键，值）
提前谢谢。

Answer 1

您可以按计算机ID进行分组，然后使用max和case选择正确的键。例如：

select  computer_id
,       max(case when key = 3 then value end) as Name
,       max(case when key = 4 then value end) as IP
,       max(case when key = 5 then value end) as User
from    YourTable
group by
        computer_id

Answer 2

CREATE VIEW your_view
AS
SELECT x.computer_id, x.value AS name, y.value AS ip_address, z.value AS user
FROM computers AS x
    INNER JOIN computers AS y
        ON x.computer_id = y.computer_id
    INNER JOIN computers AS z
        ON x.computer_id = z.computer_id
WHERE x.key = 3
    AND y.key = 4
    AND z.key = 5

Answer 3

另一个解决方案是子查询：

SELECT
    computer_id,
    value AS 'name',
    (SELECT value FROM computers sqi WHERE sqi.computer_id = computers.computer_id AND sqi.key = 4) AS 'ip',
    (SELECT value FROM computers squ WHERE squ.computer_id = computers.computer_id AND squ.key = 5) AS 'user'
FROM
   computers
WHERE
   key = 3

Answer 4

select  computer_id, 
max(case when [KEY] = 3 then value end) as Name, 
max(case when [KEY] = 4 then value end) as IP, 
max(case when [KEY] = 5 then value end) as [User]
from  YourTable
group by computer_id

Answer 5

您要查询的是遵循EAV model设计的表格。以下是article with some examples如何/需要查询EAV。

以下是表定义的子查询示例：

SELECT x.Computer_Id,
(SELECT value FROM Computers AS a WHERE x.Computer_Id = a.Computer_Id AND [key]= 3) AS 'Name',
(SELECT value FROM Computers AS b WHERE x.Computer_Id = b.Computer_Id AND [key]= 4) AS 'IpAddress',
(SELECT value FROM Computers AS c WHERE x.Computer_Id = c.Computer_Id AND [key]= 5) AS 'User'
FROM Computers as x
GROUP BY x.Computer_Id

尝试多次使用相同列时的SQL Server视图

5 个答案: