Question

I have the logic worked out, just not sure how to best write this query.

the logic is

we have a deal ID of 1
a deal is linked to multiple regions
a deal is linked to multiple interests
a user is linked to multiple regions
a user is linked to multiple interests
we want all users where….

the user is linked to the same region as a deal

userRegionLink url, dealRegionLink drl
url.regionId is in drl.regionId where drl.dealId = 1
the user is linked to the same interest as a deal
userInterestLink uil, dealInterestLink dil
uil.interestId is in dil.interestId where dil.dealId = 1
this would give us a list of the users
now we need to select distinct from the list so we only end up sending each user a single email

But I have no idea what the best way to write this query would be.

We are dealing with a few tables here

We have

users which has all the user Information in it userId and other columns not important

userInterestLink which has userId and interestId
dealInterestLink which has dealId and interestId

userRegionLink which has userId and regionId
dealRegionLink which has dealId and regionId

so what we are wanting in the end is all the user info which matches.

Answer 1

I take RC’s answer and modify it

SELECT u.userId, uil.interestId, url.regionId FROM users u 
  JOIN userInterestLink uil ON (uil.userId = u.userId) 
  JOIN userRegionLink url ON (url.userId = u.userId) 
WHERE interestId IN (
  SELECT DISTINCT interestId FROM dealInterestLink WHERE dealId = 1
) AND regionId IN (
  SELECT DISTINCT regionId FROM dealRegionLink WHERE dealId = 1
)

as there is no need for LEFT JOIN if I exclude the NULL rows afterwards.

A more “symmetric” version without subqueries and with USING would be

SELECT u.userId, uil.interestId, url.regionId FROM users u 
  JOIN userInterestLink uil USING (userId)
  JOIN userRegionLink url USING (userId)
  JOIN dealInterestLink dil USING (interestId)
  JOIN dealRegionLink drl USING (regionId, dealId)
WHERE dealId = 1

Untested as well.