Question

Table:

• activities: id, userId, description, objectId
• users: id, name
• usersFriends, id, userId, friendUserId
• objects: id, name

The current query:

   SELECT A.*, U.*
   FROM usersFriends UF
   JOIN activities A ON A.userId = UF.friendUserId
   JOIN users U ON U.id = A.userId
   WHERE A.objectId = x

The problem with the current query is that if users have matching friends for example:

• user 1: tim
• user 2: ryan
• user 3: allan
• user 4: charlie

tim is friends with charlie
ryan is friends with charlie

We get the activities of object X, but we get all the activities double because tim is friends with charlie and ryan is friends with charlie, so I need some kind of distinct?

Thanks for help!

Answer 1

I usually do like this ... AND A.userId < UF.userId

SELECT A.*, U.*
   FROM usersFriends UF
   JOIN activities A ON A.userId = UF.friendUserId AND A.userId < UF.userId
   JOIN users U ON U.id = A.userId
   WHERE A.objectId = x