SQL子查询作为自己的列

Question

考虑一下。我的表看起来像这样

ID1   |   ID2   |    Value   |
1          1         Three
1          2         Random
1          3         Words
2          1         Not
2          2         So
2          3         Random
3          1         Why
3          2         No
3          3         Yes

我的输出应该是

ID   |   Value1   |   Value2   |   Value3
1    |     Three  |    Random  |      Words
2    |     Not    |    So      |      Random
3    |     Why    |    No      |      Yes

我在找什么？我不需要解决方案，只需要寻找的概念，因为我迷失了。谢谢。

Answer 1

您要查找的概念是PIVOT或TRANSPOSE。尝试在Google中搜索“将行转换为列”。

在oracle中，您的PIVOT查询如下：

SELECT *
FROM   (SELECT ID1 ID, VALUE
        FROM   MY_TABLE)
PIVOT  (MIN(VALUE) AS VALUE FOR (ID2) IN ('1' ,'2','3'));

这是site for reference

Answer 2

试试这个。

SQL QUERY

SELECT ID1 As 'ID',
MAX(IF(ID2=1 ,Value,null)) AS 'Value1',
MAX(IF(ID2=2,Value,null)) AS 'Value2',
MAX(IF(ID2=3,Value,null)) AS 'Value3'
FROM MyTable GROUP BY ID1;

或

SELECT ID1 AS 'ID', 
[1] AS 'Value1', 
[2] AS 'Value2', 
[3] AS 'Value3'
FROM (
SELECT ID1,ID2,Value
FROM MyTable) x
PIVOT(
MAX(Value)
FOR ID2 IN ([1],[2],[3]) 
) p

<强> FIND SQL FIDDLE HERE