MySQL:将两列上的 SELECT DISTINCT 放入一个别名列中

Question

让我们承认我有这张 table

+---------+---------+
| columnA | columnB |
+---------+---------+
|       1 |       2 |
|    NULL |       3 |
|       5 |       4 |
|       1 |       5 |
|       1 |       6 |
|       2 |    NULL |
|       2 |       3 |
|       6 |       4 |
|       2 |       5 |
+---------+---------+

我想做这样的事情(将两列的不同值选择到别名列中):

SELECT DISTINCT(列A，列B)AS列C

获取此输出

+---------+
| columnC |
+---------+
|       1 |
|       2 |
|       3 |
|       4 |
|       5 |
|       6 |
+---------+

Answer 1

您可以对两列进行union查询，这(隐式)从两列返回不同的值:

SELECT columnA AS columnC FROM mytable WHERE columnA IS NOT NULL 
UNION
SELECT columnB AS columnC FROM mytable WHERE columnB IS NOT NULL 
ORDER BY columnC;