将两列c1，c2组合为表中的c3

Question

c1  c2

10  30
20  40

C1，C2是两列，我希望使用sql查询输出如下所示。

C3

10
20
30
40

Answer 1

使用UNION（隐式不同）或UNION ALL：

SELECT c1 AS c3 FROM tablename
UNION ALL
SELECT c2       FROM tablename

Answer 2

您可以使用UNION，不使用ALL关键字，查询结果只是唯一值。如果您想保留重复内容，请使用UNION ALL。

SELECT C1 as C3 FROM TABLENAME
UNION
SELECT C2 as C3 FROM TABLENAME

Answer 3

您需要使用UNION ALL查询来获得结果：

select c1 as c3
from yourtable
union all
select c2 as c3
from yourtable

请参阅SQL Fiddle with Demo

此类查询将将多列中的数据移植到多行中。

根据您使用的数据库产品，某些产品具有UNPIVOT功能，可以为您进行数据转换。例如，如果您使用的是SQL Server或Oracle，则可以使用：

select c3
from yourtable
unpivot
(
  c3 for col in (c1, c2)
) u
order by c3

请参阅SQL Fiddle with Demo

Answer 4

这将按表

保留排序

SELECT 1 AS ordering, c1 AS c3
FROM mytable
UNION
SELECT 2 AS ordering, c2 AS c3
FROM mytable
ORDER BY ordering, c3

如果您不能忽略排序列，可以将其转换为子查询

SELECT c3
FROM (
    SELECT 1 AS ordering, c1 AS c3
    FROM mytable
    UNION
    SELECT 2 AS ordering, c2 AS c3
    FROM mytable) a
ORDER BY ordering, c3