Question

I need help with a SQL Query

I have this table

likes
 friend    friend2
      1          2
      2          1
      3          1
      4          5

I need to select only one pair of the friends that like each other.

With my current select I’m obtaining this

 id     name         id     name
1709    Cassandra    1689   Gabriel 
1689    Gabriel      1709   Cassandra
1501    Jessica      1934   Kyle    
1934    Kyle         1501   Jessica 

but the expected query result is:

 id     name        id     name
1709    Cassandra   1689    Gabriel 
1501    Jessica     1934    Kyle    

Answer 1

If you are sure that every pair is entered in the database twice (once as A, B and again as B,A) then you can use this:

 SELECT friend, friend2
 FROM yourtable
 WHERE friend < friend2

If there can be some pairs that are only entered once, then you can use this:

 SELECT DISTINCT
     LEAST(friend, friend2) AS friend,
     GREATEST(friend, friend2) AS friend2
 FROM yourtable