Question

I am trying to query a database to return some matching records and can’t work out how to do it in the most efficient way. I have a TUsers table, a TJobsOffered table and a TJobsRequested table. The UserID is the primary key for the TUsers table and is used within the Job tables in a one to many relationship.

Ultimately I want to run a query that returns a list of all matching users based on a particular UserID (eg a matching user is one that has at least one matching record in both tables, eg if UserA has jobid 999 listed in TJobsOffered and UserB has jobid 999 listed in TJobsRequested then this is a match).

In order to try and get my head around it i’ve simplified it down a lot and am trying to match the records based on the jobids for the user in question, eg:

SELECT DISTINCT TJobsOffered.FUserID FROM TJobsOffered, TJobsRequested
WHERE TJobsOffered.FUserID=TJobsRequested.FUserID AND 
(TJobsRequested.FJobID='12' OR TJobsRequested.FJobID='30') AND
(TJobsOffered.FJobID='86' OR TJobsOffered.FJobID='5')

This seems to work fine and returns the correct results however when I introduce the TUsers table (so I can access user information) it starts returning incorrect results. I can’t work out why the following query doesn’t return the same results as the one listed above as surely it’s still matching the same information just with a different connector (or is the one above effectively many to many and the one below 2 sets of one to many comparisons)?

SELECT DISTINCT TUsers.Fid, TUsers.FName FROM TUsers, TJobsOffered, TJobsRequested
WHERE TUsers.Fid=TJobsRequested.FUserID AND TUsers.Fid=TJobsOffered.FUserID AND
(TJobsRequested.FJobID='12' OR TJobsRequested.FJobID='30') AND
(TJobsOffered.FJobID='86' OR TJobsOffered.FJobID='5')

If anyone could explain where i’m going wrong with the second query and how you should incorporate TUsers then that would be greatly appreciated as I can’t get my head around the join. If you are able to give me any pointers as to how I can do this all in one query by just passing the user id in then that would be massively appreciated as well! 🙂

Thanks so much,

Dave

Answer 1

Try this

SELECT DISTINCT TJobsOffered.FUserID , TUsers.FName
FROM TJobsOffered
INNER JOIN  TJobsRequested ON TJobsOffered.FUserID=TJobsRequested.FUserID
LEFT JOIN TUsers ON TUsers.Fid=TJobsOffered.FUserID
WHERE  
(TJobsRequested.FJobID (12,30) AND
(TJobsOffered.FJobID IN (86 ,5)