gistfile1.txt

#Table Friendships

+----+------------+-------------------+------------------+------------+------------+
| id | dataset_id | following_user_id | followed_user_id | created_at | deleted_at |
+----+------------+-------------------+------------------+------------+------------+
|  1 |          1 |                12 |            13348 | NULL       | NULL       |
|  2 |          1 |               107 |            13348 | NULL       | NULL       |
|  3 |          1 |               274 |            13348 | NULL       | NULL       |
|  4 |          1 |               324 |            13348 | NULL       | NULL       |
|  5 |          1 |               418 |            13348 | NULL       | NULL       |
|  6 |          1 |               422 |            13348 | NULL       | NULL       |
|  7 |          1 |               455 |            13348 | NULL       | NULL       |
|  8 |          1 |               456 |            13348 | NULL       | NULL       |
|  9 |          1 |               509 |            13348 | NULL       | NULL       |
| 10 |          1 |               544 |            13348 | NULL       | NULL       |
| 11 |          1 |                12 |            13349 | NULL       | NULL       |
| 12 |          1 |               107 |            13349 | NULL       | NULL       |
| 13 |          1 |               274 |            13349 | NULL       | NULL       |
| 14 |          1 |               324 |            13349 | NULL       | NULL       |
| 15 |          1 |               418 |            13349 | NULL       | NULL       |
| 16 |          1 |               422 |            13349 | NULL       | NULL       |
| 17 |          1 |               455 |            13350 | NULL       | NULL       |
| 18 |          1 |               456 |            13350 | NULL       | NULL       |
| 19 |          1 |               509 |            13350 | NULL       | NULL       |
| 20 |          1 |               544 |            13350 | NULL       | NULL       |
+----+------------+-------------------+------------------+------------+------------+



#With data in a structure like this, how would I be able to find out the intersections of following_user_id from followed_user_id? In other words, followed_user_id of 
#13348 and 13349 have 6 similar start_id rows (following_user_ids of 12,107,274,324,418,422), 13348 and 13350 have 4 (455,456,509,544), and 13349 
#and 13350 have zero similar rows.



#Query I have been trying: select count(a.following_user_id) from friendships as a, friendships as b, friendships as c where a.following_user_id=b.following_user_id=c.following_user_id and (a.followed_user_id=13348 and b.followed_user_id=13349 and c.followed_user_id=13350);