Question

I’ve got the following Tables:

User 1:n UserFilter n:1 Filter

Filter got an ID and a Name, User got his Name as ID (don’t blame me, not my idea!).

The whole “User ‘a’ got Filters 1, 2 and 3”-Idea is being used in an ASP frontend, not important for the question.

UserFilter simply got 2 columns, User and FilterID, so if there’s a column User a – Filter 1, that means User a is using Filter 1, if there is no such column, it means he’s not.

Now I’d like to perform a SELECT query that returns every filter (there are 8 overall) for a specific user with a custom column called active.

Here’s what I got so far:

select 
    distinct f.Name, f.Type, 
    case when uf.userid = 'a' then 1 else 0 end as Active 
from filter f 
left outer join userfilter uf on f.id = uf.filterid
where uf.userid = 'a' or uf.userid is null

This will return 8 columns, some of them with Active = 0 and some with Active = 1, just as I wanted, BUT if UserFilter contains filters of multiple users, e.g.

a - 1
a - 2
b - 3
b - 7
a - 8

and I run this query for User “a” the query will only return Filter 1 as active, 2 as active, 4 5 and 6 as inactive and 8 as active, completely leaving out 3 and 7.

Any ideas?

Thanks!

Answer 1

The condition that userid=’a’ should be a join condition:

select 
    distinct f.Name, f.Type, 
    case when uf.userid = 'a' then 1 else 0 end as Active 
from filter f 
    left outer join userfilter uf on f.id = uf.filterid and uf.userid = 'a'