两列的MYSQL不同

Question

我有两列：发送者，我的表中的接收者。 我想为发送者或接收者等于 b 的两列获取不同的值，然后将它们连接成字符串。

....................
sender  |  receiver
....................
  a            b
  c            b
  b            a
  b            c
  d            f
  b            e
  b            e
  e            b

结果集应该看起来像 a,b,c,e

我应该怎么做才能实现这一目标？

Answer 1

看看这个线程： MySQL SELECT DISTINCT multiple columns

SELECT DISTINCT value FROM
( 
    SELECT DISTINCT a AS value FROM my_table
    UNION 
    SELECT DISTINCT b AS value FROM my_table
    UNION 
    SELECT DISTINCT c AS value FROM my_table 
) AS derived

Answer 2

您只需执行 2 个联合查询即可获取值。 Union 应该消除重复项。 然后您可以将其用作子查询并对结果执行 GROUP_CONCAT：-

SELECT GROUP_CONCAT(aCol)
FROM
(
    SELECT sender AS aCol
    FROM SomeTable
    WHERE sender = 'b'
    OR receiver = 'b'
    UNION
    SELECT receiver AS aCol
    FROM SomeTable
    WHERE sender = 'b'
    OR receiver = 'b'
) sub0

Answer 3

尝试这个：

create table test (sender char(1), receiver char(1));    
insert into test values ('a','b'), ('c','b'), ('b','a'), ('b','c'), ('d','f'), ('b','e'), ('b', 'e'), ('e', 'b');

select group_concat(sender  separator ',') as result 
from (
  select sender from test where receiver = 'b' 
  union
  select 'b'
) alias;

+---------+
| result  |
+---------+
| a,c,e,b |
+---------+

如果您想要按字母顺序排序，您可以将select 'b'替换为select 'b' order by sender ，您将得到a,b,c,e作为结果