mysql查询统一2列

Question

我有一个包含4列（id，发件人，收件人，状态）的朋友，我需要一个可以统一（重聚，我不知道英文单词）发件人和收件人列的查询。 例如，表格如下所示

| sender | receiver |
|    2   |   10     |
|    2   |    8     |
|    2   |    9     |
|    6   |    2     |
|    7   |    3     |

查询应该只给出发送方和接收方的唯一ID。 （2,3,6,7,8,10）

Answer 1

这听起来像是union的工作：

select sender as id from <table_name>
union
select receiver as id from <table_name>

请注意，union会删除重复项（如果您想保留重复项，请使用union all。）

Answer 2

SELECT DISTINCT a.iResult
FROM
    (SELECT sender as iResult FROM tableName
        UNION
     SELECT receiver as iResult FROM tableName) a
ORDER BY iResult ASC

返回

2
3
6
7
8
9
10

OR

SELECT GROUP_CONCAT(b.iResult)
     (SELECT DISTINCT a.iResult
     FROM
             (SELECT sender as iResult FROM tableName
                 UNION
              SELECT receiver as iResult FROM tableName) a
         ORDER BY iResult ASC) b

返回

2,3,6,7,8,9,10