Question

Tables:

items -> id, userId, tagId, postedOn

itemsTags -> id, name

users -> id, firstName, lastName

usersFriends -> id, userId, friendUserId

The system needs a re-build, at the moment the flow is like this:

1. Get all the friends of the user.
2. Per friend (foreach) get the items the friend posted.
3. Get the tag data of the item (tagId).
4. Get the user data of the item (userId).

But the problem is, I need to sort it by date, and later on by a specific date for example, I want to see all the items of my friends that where posted today so I need a query that does those 4 queries in one, so basically SELECT * FROM usersFriends JOIN items ON userId ...

I just can’t figure out the rest.

Answer 1

SELECT F.*, I.*, IT.* 
FROM usersFriends UF 
  LEFT JOIN users F                  --- friends
    ON F.id = UF.friendUserId 
  LEFT JOIN items I                  --- items they posted
    ON I.userId = UF.friendUserId 
  LEFT JOIN itemsTags IT             --- tags of those items
    ON I.tagId = IT.id 
WHERE UF.userId = ??

Where on the questionmarks you place the user’s id.