SQL: No Sub-Query but only Joins - sql-server

Question

I am trying to find an alternative to this query where no sub-select is present but only joins (left, right, inner etc).
select count(SC.NUMBER_C)
from FNQP2PORTAL.SA.SEC_CAS SC
where SC.NUMBER_C not in (
select E.Reference from
FNQP2HQ.dbo.Entities E
join FNQP2HQ.dbo.Classes C on C.ID = E.ClassID
where C.Reference = 'Assembly case')
So, it should be something like...
select count(SC.NUMBER_C)
from FNQP2PORTAL.SA.SEC_CAS SC
left join FNQP2HQ.dbo.Entities E on E.Reference = SC.NUMBER_C and E.Reference IS NULL
inner join FNQP2HQ.dbo.Classes C on C.ID = E.ClassID and C.Reference = 'Assembly case'
Can somebody help me here?

Answer 1

The queries you posted are very different. One is inclusive (where SC.NUMBER_C IN.... - and the other is exclusive (left outer join where E.Reference is NULL). Because of these completely different queries, it's unclear what you're trying to do.
This is how you would accomplish your first query with a join instead of the subquery.
SELECT COUNT(SC.NUMBER_C)
FROM FNQP2PORTAL.SA.SEC_CAS SC
JOIN FNQP2HQ.dbo.Entities E
ON SC.NUMBER_C = E.Reference
JOIN FNQP2HQ.dbo.Classes C
ON C.ID = E.ClassID
WHERE C.Reference = 'Assembly Case'
EDIT:
You need to use a subquery and NOT IN to get what you're asking for in your comment. You can't only use joins.
SELECT COUNT(SC.NUMBER_C)
FROM FNQP2PORTAL.SA.SEC_CAS SC
WHERE SC.NUMBER_C NOT IN
(
SELECT E.Reference
FROM FNQP2HQ.dbo.Entities E
JOIN FNQP2HQ.dbo.Classes C
ON C.ID = E.ClassID
WHERE C.Reference = 'Assembly Case'
)

Answer 2

select count(SC.NUMBER_C)
from FNQP2PORTAL.SA.SEC_CAS SC
INNER JOIN FNQP2HQ.dbo.Entities E on SC.NUMBER_C = E.Reference
INNER JOIN FNQP2HQ.dbo.Classes C on C.ID = E.ClassID
where C.Reference = 'Assembly case'

Answer 3

One reason people use the WHERE IN logic is because of duplicates being returned via join. So in this case moving the logic to inner joins could result in the count inflating. Here's how you would work around that:
select count(SC.NUMBER_C)
from FNQP2PORTAL.SA.SEC_CAS SC
inner join
(
select distinct E.Reference
from FNQP2HQ.dbo.Entities E
join FNQP2HQ.dbo.Classes C on C.ID = E.ClassID
where C.Reference = 'Assembly case'
) as b
on b.reference = sc.NUMBER_C

Answer 4

Try the below code , it may throw error as you have not share the sample data with us. But you should use exists clause.
SELECT COUNT(SC.NUMBER_C)
FROM FNQP2PORTAL.SA.SEC_CAS SC,
FNQP2HQ.dbo.Classes C,
FNQP2HQ.dbo.Entities E
WHERE C.ID = E.ClassID
AND C.Reference = 'Assembly Case'
and not exists(
select 1 from FNQP2HQ.dbo.Entities E1
ON SC.NUMBER_C = E1.Reference)