如何编写以下SQL查询

Question

这是我的表结构

在发布此问题之前，我尝试过此操作：

select x.col1,x.col2 from 
(
(select A from #t union all select C from #t) col1,
(select B from #t union all select D from #t) col2
)as x 

Answer 1

您可以这样尝试。

Select A,B FROM #T
UNION ALL
Select C,D FROM #T WHERE C is not null

Answer 2

我会做

SELECT T1.A AS A_or_C, T1.B AS B_or_D FROM table_name T1
UNION
SELECT T2.C AS A_or_C, T2.D AS B_or_D FROM table_name T2

如此绝对清楚。

干杯

Answer 3

select A, B from TABLE union select C, D from TABLE

Answer 4

select A, B from table_name
union 
select C,D from table_name

Answer 5

尝试这个：

SELECT A as Name,B as Value FROM x
UNION ALL
SELECT C,D FROM x 
WHERE C IS NOT NULL

结果将是：

NAME    VALUE
AA      0.5
BB      0.5
CC      0.3
DD      0.2
BB      0.3
CC      0.5

请参见SQL Fiddle中的结果