Question

I’m trying to do a self join on this query and keep getting the error invalid object name x

select row_number() over(order by patientid,admissiondate, claimsfromdate,datediff(dd,admissiondate, claimsfromdate)) as rn
    ,x.patientid, x.admissiondate, x.claimsfromdate, x.rehabwait

from
(
SELECT distinct 
        patientid
        ,admissiondate
        ,claimsfromdate
        ,DATEDIFF(dd, admissiondate, claimsfromdate) as rehabWait, hcpcs
FROM    Claims
WHERE   hcpcs in ('g0151', '97001', '97002', '9339') and claimsfromdate > admissiondate
) x inner join x as x2 on x.patientid=x2.patientid

I can’t do this without saving it as a view or rewriting the query out twice (once in the from, once in the inner join), can I?

Answer 1

Use a CTE:

with x as (
     SELECT distinct patientid, admissiondate, claimsfromdate,
            DATEDIFF(dd, admissiondate, claimsfromdate) as rehabWait, hcpcs
     FROM    Claims
     WHERE   hcpcs in ('g0151', '97001', '97002', '9339') and
             claimsfromdate > admissiondate
    )
select row_number() over (order by patientid, admissiondate,
                                   claimsfromdate,
                                   datediff(dd,admissiondate, claimsfromdate)
                         ) as rn,
       x.patientid, x.admissiondate, x.claimsfromdate, x.rehabwait
from x inner join
     x as x2
     on x.patientid=x2.patientid

Having fixed your original problem, I do not see what you are using x2 for. It doesn’t appear in the “SELECT” statement. All you are doing is creating a cross product of all claims for a given patient. Perhaps this is reasonable. I would expect a group by to be part of such a query.