Question

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

我想创建一个查询来获取此信息：

ID  Amount  Type
1   5       T1
2   10      T2

正如您所看到的，可能有多种（ID，Key）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

但我得到的结果是我没想到的

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

我已经阅读过这篇文章，但它不适用于我的案例，尽管它有助于here

有关谁解决这个问题的想法？

Answer 1

SELECT 
  id, amount, type
FROM TABLE1
  natural join (SELECT ID, MAX(SEQ) as SEQ FROM TABLE1 GROUP BY ID) 
pivot (
  max(VALUE) for key in ('Amount' as amount, 'Type' as type)
)

fiddle

Answer 2

the linked question中遗漏的内容是DISTINCT关键字。

另请参阅下面的解释the query posted by ypercube。事实上，你正在获得重复，因为你自己加入了一个表。因此，行将被镜像。

你的子查询应该是：

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

Answer 3

我意识到还有另一个专栏，我没有提出影响结果的问题（以避免发出实际数据）。唯一约束是（ID，Key，Seq，Time）而不是（ID，Key，Seq）。正如@Andrew提到的那样，查询返回了正确的结果。

再次进行查询

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sqlfiddle。如果我浪费了任何人的时间，我道歉。

从表中选择值作为列标题

3 个答案: