How do I put two conditions in having in SQL Server? - sql

Question

I have to get members that are on five different groups and those groups should have 5 members each
Member (idMember, nameMember)
Group (idGroup)
Belongs (idMember, idGroup)
Groups have members, members are in groups, a member can be in as many groups as he wants but a member can't be twice on the same group
I made something like
select idMember, nameMember
from Member m, Group g
where idMember in (select b.idMember
from Belongs b)
group by idMember, nameMember
having (select count(*)
from Belongs b
where b.idMember = m.idMember)>5
and
(select count (*)
from Belongs b
where b.idGroup = g.idGroup /*??*/)>5
and there I don't know how to relate belongs with group

Answer 1

Approach this type of problem in steps. The following gets the members that are in five groups:
select b.idMember
from belongs b -- Note: `group` is a reserved word so a bad name for a table
group by b.idMember
having count(*) = 5;
The following gets the groups that have five members:
select b.idGroup
from belongs b
group by b.idGroup
having count(*) = 5;
(Interesting symmetry.)
If you want to limit the first query to the groups in the second, then a simple way is to use in:
select b.idMember
from belongs b
where b.groupId in (select g.idGroup
from belongs b
group by b.idGroup
having count(*) = 5
)
group by b.idMember
having count(*) = 5;
When you are dealing with complex queries, build them up one step at a time.
Note: group is a really bad name for a table because it is a reserved word. And, if you want the table name then use JOIN to join to the members table to get the right name.
EDIT:
You can use join to get columns from member:
select b.idMember, m.name
from belongs b join
member m
on b.idMember = m.idMember
where b.groupId in (select g.idGroup
from belongs b
group by b.idGroup
having count(*) = 5
)
group by b.idMember, m.name
having count(*) = 5;