Sql 从表中选择值作为列标题

我有一个具有以下结构的表：

ID  KEY     VALUE   SEQ
1   Amount  5       2   
1   Amount  4       1
1   Type    T1      2   
1   Type    T1      1
2   Amount  10      2   
2   Amount  5       1
2   Type    T2      2
2   Type    T2      1

我想创建一个查询以获取以下信息：

ID  Amount  Type
1   5       T1
2   10      T2

正如您所看到的，（ID，Key）可以有多种组合，但（ID，Key，Seq）是唯一的

SELECT  T.ID, 
        T1.VALUE as Amount, 
        T2.VALUE as Type
FROM 
    (SELECT ID, MAX(SEQ) as MAXSEQ FROM TABLE GROUP BY ID) as T
    JOIN
        TABLE as T1
            ON T1.ID = T.ID
            AND T1.KEY = 'Amount'
            AND T1.SEQ = MAXSEQ
    JOIN
        TABLE as T2
            ON T2.ID = T.ID
            AND T2.KEY = 'Type'
            AND T2.SEQ = MAXSEQ

但是我得到了我没有预料到的结果

ID  Amount  Type

    1   5       T1
    1   4       T1
    1   10      T1
    1   5       T1
    2   10      T2
    2   5       T2
    2   4       T2
    2   5       T2

我已经读过这篇文章，但它不适用于我的情况，虽然它有帮助

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你知道该由谁来解决这个问题吗？

你缺少的是

DISTINCT

关键字

另请参见下面的解释。事实上，您得到的是重复的，因为您正在加入一个表本身。因此，行将被镜像

您的子查询应该是：

(SELECT DISTINCT ID, MAX(SEQ) as MAXSEQ FROM TABLE GROUP BY ID) as T

---

我意识到还有另外一个专栏，我没有提出这个问题（为了避免给出真实数据），这影响了结果。唯一的约束是（ID，Key，Seq，Time），而不是（ID，Key，Seq）。正如@Andrew提到的，查询返回的是正确的结果

问题又来了

SELECT  T.ID, 
        T1.VALUE as Amount, 
        T2.VALUE as Type
FROM 
    (SELECT ID, MAX(SEQ) as MAXSEQ FROM TABLE GROUP BY ID) as T
    JOIN
        TABLE as T1
            ON T1.ID = T.ID
            AND T1.KEY = 'Amount'
            AND T1.SEQ = MAXSEQ
    JOIN
        TABLE as T2
            ON T2.ID = T.ID
            AND T2.KEY = 'Type'
            AND T2.SEQ = MAXSEQ

---

感谢Andrew的澄清和支持。如果我浪费了任何人的时间，我表示歉意。

我想我得到了想要的结果。我有什么误解吗？谢谢你的评论安德鲁。。您正在示例中使用sql server。我用的是oraclenot真的。通过按id分组，我将获得与DISTINCT相同的效果。

SELECT  T.ID, 
        T1.VALUE as Amount, 
        T2.VALUE as Type
FROM 
    (SELECT ID, MAX(SEQ) as MAXSEQ FROM TABLE GROUP BY ID) as T
    JOIN
        TABLE as T1
            ON T1.ID = T.ID
            AND T1.KEY = 'Amount'
            AND T1.SEQ = MAXSEQ
    JOIN
        TABLE as T2
            ON T2.ID = T.ID
            AND T2.KEY = 'Type'
            AND T2.SEQ = MAXSEQ