Question

I have a simple message schema where a “thread” ties 2 or more users to a stream of messages. Each message belongs to a single thread. It works just like SMS messages, or Facebook messages.

Given a string (representing a name or partial name of a user), I need a query that will find all threads that match where:

1. the current user (userID) is a member of the thread
2. the name or partial name of a user is also a member of the thread

Here are my tables:

MessageThreads:
threadID
lastUpdated

MessageThreadUsers:
threadFK
userFK

Users
userID
userFirstName
userLastName
userFullName

This query gets all threads that the current user belongs to:

SELECT DISTINCT threadFK FROM MessageThreadUsers
WHERE userFK = 'usr_developer'

But how would I join each thread with all users in the thread (not including the current user) that match by name or partial name?

Answer 1

This should show you the other users of all threads that the ‘usr_developer’ key is part of.

    SELECT MT.ThreadId, U.userID, U.userFullName
      FROM MessageThreads MT 

INNER JOIN MessageThreadUsers MTCU on (MTCU.threadFK = MT.threadID)
INNER JOIN Users CU on (MTCU.userFK = CU.userID and CU.userID = 'usr_developer')

INNER JOIN MessageThreadUsers MTU on (MTU.threadFK = MT.threadID)
INNER JOIN Users U on (MTU.userFK = U.userID and U.userID <> 'usr_developer') 

     WHERE U.UserFullName like '%John%' -- Do your filters here

This joins against the tables twice, first, we join to the users table to only pull back the set of threads that have a user with the id of ‘usr_developer’. Then we join the resulting threads against the users table again, this time where the user id is not usr_developer. Finally we can filter the result set by the name.