Question

I have a need to build a MySQL query to notify users of a software package when a comment is added to a post. The tables I have for this are

Posts: pid, uid

Comments: cid, uid, pid

Users: uid

Related: rid, uid1, uid2

Devices: did, uid

A post can have many comments, many comments can be posted per user, and a user may have many devices.

When a comment is inserted I need to get a list of unique devices for everyone who has contributed to the comments for the moment including the author but only where they are related to the user who has commented.

the

redlated.uid1

holds the userid and

related.uid2

holds their related userid e.g.

-----------------------------------
| rid       |  uid1      |  uid2  |
-----------------------------------
| 1         |  34        |  43    |
-----------------------------------
| 2         |  43        |  34    |
-----------------------------------

I have available the following data

PostAuthorId | PostID | UserID

Can anyone help I am struggling to get the right data out all queries thus far have been wrong, i have not posted one as I think it could confuse even further.

As i said I need to return only unique devices, any help would be awesome thanks

EDIT SQLFIDDLE **

http://sqlfiddle.com/#!2/4217f

---

Answer 1

All you need is one correct (multi) JOIN

SELECT ...
FROM Posts P
INNER JOIN Users O ON P.uid = O.uid  -- Post owner
INNER JOIN Devices OD ON O.uid = OD.uid  -- Devices of post owner
INNER JOIN Related R ON O.uid = R.uid1  -- Post owner to other user relationship
INNER JOIN Comments C ON R.uid2 = C.uid AND P.pid = C.pid  -- Comments by related user
INNER JOIN Devices CD ON C.uid = CD.uid  -- Devices of users posting comments
WHERE pid = yourPostID

this should do it.
Don’t forget that you have Devices table twice so you have to refer to them via OD (owner’s) and CD (comment poster’s) devices