Question

relationID     sessionID_Ref     userID_Ref
1              1                 1
2              1                 2
3              2                 1
4              2                 3
5              3                 1
6              3                 2
7              3                 3

Okey! I’m building a messaging system with the possibility to send messages to a group of people. But I’m stuck with this SQL query where to find the sessionID depending on what users I send the message to.

For example: If I (userID: 1) send a message to userID 2, the SQL Query should return sessionID: 1

If I send a message to userID 2 and 3, it sould return: sessionID: 3

Can I do this with a single sql query, using MSSQL?

Answer 1

Possibly something like this:

select sessionID_Ref
from tablename
group by sessionID_Ref
having count(distinct userID_Ref) = 2
   and min(userID_Ref) = 1
   and max(userID_Ref) = 2

---

Here’s a full example:

create table #tablename (
    relationID int,
    sessionID_Ref int,
    userID_Ref int
)

insert into #tablename values(1,1,1)
insert into #tablename values(2,1,2)
insert into #tablename values(3,2,1)
insert into #tablename values(4,2,3)
insert into #tablename values(5,3,1)
insert into #tablename values(6,3,2)
insert into #tablename values(7,3,3)


create table #users (
    users int
)

insert into #users values(1)
insert into #users values(3)


select t.sessionID_Ref from #tablename t
inner join #users u on t.userID_Ref = u.users
inner join (
    select t.sessionID_Ref
    from #tablename t
    group by t.sessionID_Ref
    having COUNT(t.userID_Ref) = (select COUNT(*) from #users)
) aux on aux.sessionID_Ref = t.sessionID_Ref
group by t.sessionID_Ref
having COUNT(t.userID_Ref) = (select COUNT(*) from #users)


drop table #tablename
drop table #users