Question

I have two tables:

t1
____________
projectID
userID
projectExpiration

t2
____________
usrID
subscriptioID
subscriptionExpiration

I need to select porject ID from T1 where the following conditions are met:

t1.projectExpiration = older then 3 months
t2.subscriptioID = '5'
t2.expiration = older then 3 months

The user may have other subscriptions in t2. I need ONLY the results where they have a single subscription entry which has an ID of ‘5’

I need help putting it all together.

Here’s what I’ve got so far:

SELECT projectID
FROM t1
LEFT JOIN t2 ON (t1.userID = t2.userID)
WHERE t1.projectExpiration < (CURDATE() - INTERVAL 3 MONTH)
  AND t2.subscriptionExpiration = 5
      AND t2.subscriptionExpiration < (CURDATE() - INTERVAL 3 MONTH)

Feel like I’m stuck…

Answer 1

You want a not exists check to make sure 5 is the only row:

select
    *
from
    t1 x
    inner join t2 y on
        x.userid = y.userid
where
    x.projectexpiration < curdate() - interval 3 month
    and y.subscriptionid = 5
    and not exists (
        select
            1
        from
            t2 z
        where
            z.userid = x.userid
            and z.subscriptionid <> 5
    )

I should also mention that I used an inner join in lieu of a left join here. This is because you don’t want to grab rows where a t2 row doesn’t exist (you’re otherwise not accounting for nulls in your where clause). So, it’s just needless overhead. An inner join gets us down to the result set you want in a much clearer fashion.