两列的MYSQL不同

Question

I got two columns: sender, receiver in my table. I want to get the distinct for both column where sender or receiver equal to b and then concat them into string.

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

The result set should look like a,b,c,e

What should I do to achieve this?

Answer 1

Take a look at this thread : 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

You can just do 2 unioned queries to get the values. Union should eliminate the duplicates. Then you can use that as a sub query and do a GROUP_CONCAT on the results:-

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

Try this:

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 |
+---------+

If you want alphabetical ordering, you can replace select 'b' with select 'b' order by sender and you will get a,b,c,e as the result