选择与两列不同

Question

我的数据库如下：表名：消息

| receive | transmit |
---------------------
|   1    |  5    |
|   1    |  6    |
|   1    |  3    |
|   3    |  1    |
|   4    |  1    |
|   2    |  3    |
|   4    |  6    |
|   7    |  9    |

我正试图从每张桌子中获取所有唯一身份证。所以我的回答必须是1,3,4,5,6。

如果我使用SELECT DISTINCT receive FROM messages ;，我将获得1,3,4

如果我使用SELECT DISTINCT transmit FROM messages ;，我将获得1,3,5,6

我如何获得1,3,4,5,6？

Answer 1

UNION的默认值为DISTINCT：

SELECT "from" FROM tableX 
UNION
SELECT "to" FROM tableX;

Answer 2

SELECT DISTINCT `fr_om` FROM `table`
UNION
SELECT DISTINCT `to` FROM `table` WHERE `to` NOT IN (SELECT DISTINCT `fr_om` FROM table)

已更新：您只需使用UNION即可从结果集中删除重复项。

SELECT DISTINCT `fr_om` FROM `table`
UNION
SELECT DISTINCT `to` FROM `table`