Question

My where exists clause isn’t working. What trivial thing am I missing?

select * from patient as p
where exists
(
    select p.patientid, count(*) from tblclaims as c 
    inner join patient as p on p.patientid=c.patientid
    and p.admissiondate = c.admissiondate
    and p.dischargedate = c.dischargedate
    group by p.patientid
    having count(*)>500
)

patient and tblclaims are joined together by the three-field composite key as as you can see in the query.

Answer 1

The count(*) from tblclaims as c is unnecessary and could be throwing the query off.

Also, you have no WHERE clause joining patient p to your exists clause.

Not to mention you use p as an alias in both the main query and the exists clause, which is just confusing.

You probably want something like:

select * from patient
where exists
(
    select p.patientid 
    from tblclaims as c 
    inner join patient as p on p.patientid=c.patientid
        and p.admissiondate = c.admissiondate
        and p.dischargedate = c.dischargedate
    where patient.patientid = p.patientid
    group by p.patientid
    having count(*)>500
)