Question

I am trying to rework a query so that it uses standard joins (in from clause) and not the old version (migrating to SQL server so forced to do this conversion). The problem I am running into is that my version of the query below returns a lot fewer records than the original. So I am thinking one of my outer joins isn’t so outer. Thanks for any help, especially if you actually make it through the whole query. I can’t seem to find any good documentation on how to make a transition like this.

declare
@startdate datetime, @enddate datetime

select @startdate = dateadd(dd,-6,convert(datetime,convert(varchar,getdate(),101))) 
select @enddate = dateadd(dd,6,@startdate) 

SELECT PAT.CUSID as ID , 
       substring(CPTREC.CompletedDateTime,1,12) AS DateOfService, 
       SUBSTRING(PCMH.ProcedureCode,CHARINDEX('-',PCMH.ProcedureCode)+ 1,50) AS CPT_Code 
FROM cpt_records as CPTREC
left Outer Join ProcedureCodeMH as PCMH 
    on CPTREC.ProcedureCodeRevCount = PCMH.ProcedureCodeRevCount 
        and CPTREC.ProcedureCodeSer= PCMH.ProcedureCodeSer
left outer join Credit as CR 
    on CPTREC.ActInstProcCodeSer = CR.ActInstProcCodeSer 
        and CPTREC.ActInstProcCodeRevCount = CR.ActInstProcCodeRevCount
inner join ActivityInstance as ACTIN 
    on CPTREC.ActivityInstanceSer= ACTIN.ActivityInstanceSer 
        and CPTREC.ActivityInstanceRevCount = ACTIN.ActivityInstanceRevCount
inner join ActivityCapture as ACTCAP 
    on ACTCAP.ActivityInstanceSer= ACTIN.ActivityInstanceSer 
        and ACTCAP.ActivityInstanceRevCount = ACTIN.ActivityInstanceRevCount
inner join ActCaptDiagnosisMH as ACTCAPDMH 
    on ACTCAPDMH.ActivityCaptureSer = ACTCAP.ActivityCaptureSer 
        and ACTCAPDMH.ActivityCaptureRevCount=ACTCAP.ActivityCaptureRevCount
left outer join Department as DEPT 
    on ACTCAP.DepartmentSer = DEPT.DepartmentSer
left outer join Hospitality as HOSP 
    on DEPT.HospitalitySer = HOSP.HospitalitySer
Left outer join Diagnosis as DIAG 
    on ACTCAPDMH.DiagnosisSer = DIAG.DiagnosisSer
inner join TemplateCycle as TEMPCYC 
    on ACTIN.TemplateCycleSer= TEMPCYC.TemplateCycleSer
inner join Template as PLATE 
    on TEMPCYC.TemplateSer = PLATE.TemplateSer
inner join Patent as PAT 
    on PLATE.PatentSer = PAT.PatentSer
Left Outer Join PatentParticular as PATPAR 
    on PAT.PatentSer = PATPAR.PatentSer
inner join PatentDoctor as PATDOC 
    on PAT.PatentSer = PATDOC.PatentSer
inner join Doctor as DOC 
    on PATDOC.ResourceSer = DOC.ResourceSer
WHERE ( CPTREC.CompletedDateTime >= @startdate ) 
    and ( CPTREC.CompletedDateTime < dateadd(dd,1,@enddate) ) 
    and ( CPTREC.ObjectStatus = 'Active' ) 
    and ( PATDOC.OncologistFlag = 0 ) 
    and ( PATDOC.PrimaryFlag = 1 ) 
    and ( PCMH.ProcedureCode like '%77781%' 
            or PCMH.ProcedureCode like '%77782%' 
            or PCMH.ProcedureCode like '%77783%' 
            or PCMH.ProcedureCode like '%77784%' 
            or PCMH.ProcedureCode like '%77785%' 
            or PCMH.ProcedureCode like '%77786%' 
            or PCMH.ProcedureCode like '%77787%')

---

the origional that brings back more records is

---

SELECT PAT.CUSID as ID , substring(cpt_records.CompletedDateTime,1,12) AS DateOfService, SUBSTRING(ProcedureCodeMH.ProcedureCode,CHARINDEX('-',ProcedureCodeMH.ProcedureCode)+ 1,50) AS CPT_Code INTO cpt777 FROM cpt_records , ActivityCapture , ActivityInstance , Patent as PAT, ProcedureCodeMH , Template , TemplateCycle , Department , Hospitalityity , Credit , Doctor, PatentDoctor , ActCaptDiagnosisMH , Diagnosis , PatentParticular WHERE ( #cpt_records.ProcedureCodeSer *= ProcedureCodeMH.ProcedureCodeSer) and

( ProcedureCodeMH.ProcedureCodeRevCount =*cpt_records.ProcedureCodeRevCount) and

( ActivityCapture.DepartmentSer *= Department.DepartmentSer) and

( Department.HospitalitySer *= Hospitality.HospitalitySer) and

( ActivityCapture.ActivityCaptureSer *= Credit.ActivityCaptureSer) and

( ActivityCapture.ActivityCaptureRevCount *= Credit.ActivityCaptureRevCount) and

( Credit.ActInstProcCodeSer =* cpt_records.ActInstProcCodeSer) and

( Credit.ActInstProcCodeRevCount =* cpt_records.ActInstProcCodeRevCount) and

( Patent.PatentSer *= PatentParticular.PatentSer) and

( cpt_records.ActivityInstanceSer = ActivityInstance.ActivityInstanceSer ) and

(cpt_records.ActivityInstanceRevCount = ActivityInstance.ActivityInstanceRevCount ) and

( ActivityInstance.ActivityInstanceSer = ActivityCapture.ActivityInstanceSer ) and

( ActivityInstance.ActivityInstanceRevCount = ActivityCapture.ActivityInstanceRevCount ) and

( Patent.PatentSer = Template.PatentSer ) and

( Template.TemplateSer = TemplateCycle.TemplateSer ) and

( TemplateCycle.TemplateCycleSer = ActivityInstance.TemplateCycleSer ) and

( Patent.PatentSer = PatentDoctor.PatentSer ) and

( PatentDoctor.ResourceSer = Doctor.ResourceSer ) and

( ActivityCapture.ActivityCaptureSer = ActCaptDiagnosisMH.ActivityCaptureSer ) and

( ActivityCapture.ActivityCaptureRevCount = ActCaptDiagnosisMH.ActivityCaptureRevCount ) and (cpt_records.CompletedDateTime >= @startdate ) and

( cpt_records.CompletedDateTime < dateadd(dd,1,@enddate) ) and

( cpt_records.ObjectStatus = 'Active' ) and

( PatentDoctor.OncologistFlag = 0 ) and

( PatentDoctor.PrimaryFlag = 1 ) and

( ActCaptDiagnosisMH.DiagnosisSer *= Diagnosis.DiagnosisSer) and

( ProcedureCodeMH.ProcedureCode like '%77781%' or ProcedureCodeMH.ProcedureCode like '%77782%' or ProcedureCodeMH.ProcedureCode like '%77783%' or ProcedureCodeMH.ProcedureCode like '%77784%' or ProcedureCodeMH.ProcedureCode like '%77785%' or ProcedureCodeMH.ProcedureCode like '%77786%' or ProcedureCodeMH.ProcedureCode like '%77787%')

Answer 1

The problem is that a left join returns nulls for the joined column values where no matching row is found, but you are checking those column values in the where clause, but the where predicates are is executed after all the rows are joined, so they’ll never match and your outer joins are sunk.

ie, this example query:

select *
from table1 t1
left join table2 t2 on t2.fk = t1.id
where t2.col1 = 'x'

will never return any rows that don’t have corresponding rows in table2, because col1 will be null, and comparisons with null are always false, except for col1 is null.

To fix this, you need to move the tests into the ON clause, so the comparison happens while the join is being made, like this:

select *
from table1 t1
left join table2 t2 on t2.fk = t1.id and t2.col1 = 'x'

Now the left join will still return rows while matching on the key, and applying extra predicates to further refine the match.

In your case, you are doing an outer (ie left) join to ProcedureCodeMH as PCMH, but testing the columns of PCMH in the WHERE clause, similar to the first example above.

The rewrite of your query would then be (see in-line comment for where the change is):

SELECT PAT.CUSID as ID , 
       substring(CPTREC.CompletedDateTime,1,12) AS DateOfService, 
       SUBSTRING(PCMH.ProcedureCode,CHARINDEX('-',PCMH.ProcedureCode)+ 1,50) AS CPT_Code 
FROM cpt_records as CPTREC
left Outer Join ProcedureCodeMH as PCMH 
    on CPTREC.ProcedureCodeRevCount = PCMH.ProcedureCodeRevCount 
        and CPTREC.ProcedureCodeSer= PCMH.ProcedureCodeSer
        -- MOVED THIS TEST FROM WHERE CLAUSE TO HERE
        and ( PCMH.ProcedureCode like '%77781%' 
                or PCMH.ProcedureCode like '%77782%' 
                or PCMH.ProcedureCode like '%77783%' 
                or PCMH.ProcedureCode like '%77784%' 
                or PCMH.ProcedureCode like '%77785%' 
                or PCMH.ProcedureCode like '%77786%' 
            or PCMH.ProcedureCode like '%77787%')
left outer join Credit as CR 
    on CPTREC.ActInstProcCodeSer = CR.ActInstProcCodeSer 
        and CPTREC.ActInstProcCodeRevCount = CR.ActInstProcCodeRevCount
inner join ActivityInstance as ACTIN 
    on CPTREC.ActivityInstanceSer= ACTIN.ActivityInstanceSer 
        and CPTREC.ActivityInstanceRevCount = ACTIN.ActivityInstanceRevCount
inner join ActivityCapture as ACTCAP 
    on ACTCAP.ActivityInstanceSer= ACTIN.ActivityInstanceSer 
        and ACTCAP.ActivityInstanceRevCount = ACTIN.ActivityInstanceRevCount
inner join ActCaptDiagnosisMH as ACTCAPDMH 
    on ACTCAPDMH.ActivityCaptureSer = ACTCAP.ActivityCaptureSer 
        and ACTCAPDMH.ActivityCaptureRevCount=ACTCAP.ActivityCaptureRevCount
left outer join Department as DEPT 
    on ACTCAP.DepartmentSer = DEPT.DepartmentSer
left outer join Hospitality as HOSP 
    on DEPT.HospitalitySer = HOSP.HospitalitySer
Left outer join Diagnosis as DIAG 
    on ACTCAPDMH.DiagnosisSer = DIAG.DiagnosisSer
inner join TemplateCycle as TEMPCYC 
    on ACTIN.TemplateCycleSer= TEMPCYC.TemplateCycleSer
inner join Template as PLATE 
    on TEMPCYC.TemplateSer = PLATE.TemplateSer
inner join Patent as PAT 
    on PLATE.PatentSer = PAT.PatentSer
Left Outer Join PatentParticular as PATPAR 
    on PAT.PatentSer = PATPAR.PatentSer
inner join PatentDoctor as PATDOC 
    on PAT.PatentSer = PATDOC.PatentSer
inner join Doctor as DOC 
    on PATDOC.ResourceSer = DOC.ResourceSer
WHERE CPTREC.CompletedDateTime >= @startdate
and CPTREC.CompletedDateTime < dateadd(dd,1,@enddate)
and CPTREC.ObjectStatus = 'Active'
and PATDOC.OncologistFlag = 0
and PATDOC.PrimaryFlag = 1

Note: inner join can be simplified to simply join – inner is the default join type.