SQL:将行拆分为两行

Question

我有一张看起来像这样的桌子

|  ID  |   item1   |   item 2  | 
|   1  |     A1    |     B1    |
|   2  |     A2    |     B2    |

我希望得到这样的东西:

|  ID  |   item  |
|   1  |    A1   |
|   1  |    B1   |
|   2  |    A2   |
|   2  |    B2   |

在某种意义上,它与这个SO问题相反.

Answer 1

用途UNION ALL:

SELECT ID, item1 AS item
FROM mytable

UNION ALL

SELECT ID, item2 AS item
FROM mytable
ORDER BY ID, item