Question

team1
+----------+----------+
| id1      | name     |
+----------+----------+
| 1        | a        |
| 2        | b        |
| 3        | c        |
+----------+----------+

team2
+----------+----------+
| id2      | name     |
+----------+----------+
| 1        | d        |
| 2        | e        |
| 3        | f        |
+----------+----------+

play
+----------+----------+----------+
| id3      | id1      | id2      |
+----------+----------+----------+
| 1        | 1        | 1        |
| 2        | 1        | 3        |
| 3        | 2        | 1        |
| 4        | 3        | 2        |
| 5        | 2        | 3        |
+----------+----------+----------+

I’m new to sql. I am struggling with how to set a counting condition. Let’s say for the tables above, I want to find a player from team1 who plays with a player from team2 that has played or will play at least two times total. So basically, if a value from id2 shows up more than once, then any value from id1 that plays against id2 should be part of the result. Just by looking at the table, I would want it to return id1 = 1 and id1 = 2 if it was without redundancies. I can’t wrap my head around how to go about this.

Answer 1

Try:

select distinct p1.id1
from play p1
join (select id2
      from play
      group by id2
      having count(*) > 1) p2
on p1.id2 = p2.id2