Question

I have a dilemma.

Let’s assume(for simplicity’s sake) I have four tables, with different numbers of columns and rows, they are: users, mail, events and service.

When I receive a request, I have an ID that links on three of those tables, but with different columns it matches to.
Let’s say, users matches on user_id, mail matches on user_ref and events matches on user_ref as well.

That would’ve been a fine query for me to write up, even with single, multiple or even all IDs.
The problem arrives on the next step I have to take, and that’s the *service table.

The service table doesn’t conform to the same standards of the others, thus it does not have an user_id, or user_ref that can be pulled.
What it has instead, is a *mail_ref* column, and it has the potential to contain duplicates.
My current method is trying to use an IN() method, but it only works for selecting a single user/row.

Here’s my current query:

SELECT
    u.Name as Name,
    COUNT(m.user_ref) AS Mail_total,
    e.mail_id,
    COUNT(e.user_ref) AS Event_total,
    COUNT(s.mail_ref) AS service_total
FROM
    users u
LEFT JOIN
    mail m ON m.user_ref = u.user_id
LEFT JOIN
    service s ON s.mail_ref IN(e.mail_id)
LEFT JOIN 
    events e ON e.user_ref = u.user_id
WHERE u.user_id IN(my,list,of,ids)
GROUP BY s.mail_ref

The problem I have with it currently, is that although it’s selecting the correct data, it’s not selecting unique data for every id I specify.
It works marginally fine when given a single id, but as mentioned above, not when it has to retrieve multiple rows.

If anyone could help me out it would be much appreciated.

Answer 1

Do a subquery in the left join for service. Instead of:

LEFT JOIN
service s ON s.mail_ref IN(e.mail_id)

Try

LEFT JOIN
(select TOP 1 mail_ref from server) as S on s.mail_ref = e.mail_id

See if that works.