Question

我有几张表如下 -

表1：

A B C D <<Columns
1 2 3 4 <<single row

表2：

W X Y Z << Columns
5 6 7 8 << Single row

我希望将这两个表组合在一起，它会给我以下结果

结果：

P Q R S << Column headers
1 2 3 4 << row from table1
5 6 7 8 << row from table2

预期结果的列标题为P，Q，R，S和table1中的行以及table2中的行

如何使用SQL实现此目的？

Answer 1

_更新更严格，更完整，感谢@AntDC（和@Matt）和@Dudu Markovitz __

将UNION与别名一起使用，如下所示：

SELECT A AS P, B AS Q, C AS R, D AS S
FROM table1
UNION
-- or UNION ALL if you want to keep duplicate rows
SELECT W, X, Y, Z
FROM table2

Answer 2

UNION ALL 不会消除重复
在集合操作（UNION / INTERSECT / EXCEPT）中，别名取自第一个查询（目前我只知道一个例外 - Hive要求所有查询的别名都相同 - 我认为这是一个bug ）

select  A as P, B as Q, C as R, D as S
from    table1

union all

select  W,X,Y,Z
from    table2

+---+---+---+---+
| p | q | r | s |
+---+---+---+---+
| 1 | 2 | 3 | 4 |
| 5 | 6 | 7 | 8 |
+---+---+---+---+

table2 with 3 Columns

select  B as Q, C as R, D as S
from    table1

union all

select  X,Y,Z
from    table2

+---+---+---+
| q | r | s |
+---+---+---+
| 2 | 3 | 4 |
| 6 | 7 | 8 |
+---+---+---+

或

select  A as P, B as Q, C as R, D as S
from    table1

union all

select  null,X,Y,Z
from    table2

+--------+---+---+---+
|   p    | q | r | s |
+--------+---+---+---+
| 1      | 2 | 3 | 4 |
| (null) | 6 | 7 | 8 |
+--------+---+---+---+