子查询更快地加入

Question

I'm attempting to do a single query for a report that I need and I'm not sure how to get past a speed issue.

Expected Outcome
I need to have a single row per patient that lists all of their diagnosis codes in a the same column. My code does work and gets the job done but it increases my runs which must be done 30 times under different criteria and will make a 5 minute process about 30.

Attempted Resolution
I am using the following code to left outer join to.

left outer join (Select distinct add2.VisitID, 
substring((Select ', '+add1.Diagnosis  AS [text()]  
From AbsDrgDiagnoses add1 Where add1.VisitID = add2.VisitID 
ORDER BY add1.VisitID,DiagnosisSeqID For XML PATH ('')), 2, 1000) DiagText
From [Livendb].[dbo].[AbsDrgDiagnoses] add2) add3 on diag.VisitID = add3.VisitID  

Outcome
This works but my 9 second query over a month of data with only a filter one 1 of 30 codes raises to 1m 12s. If I run the query by itself it takes 3m 49s seconds to compile so its an improvement in my main table but I would like to slim this down if possible.

Other Attempted Resolutions
I attempted to create a view from the query and use that but received the same run time.

I also attached SourceID which is always the same value but my 8 tables use this in their index but it actually slightly increased my time.

Conclusion
The table that I need to merge contains around 30 million rows which is most likely the issue and there is no way around the increased time, but I'm hoping someone may have a trick that could help me decrease this time.

Answer 1

This is your subquery:

(Select distinct add2.VisitID,
       substring((Select ', '+add1.Diagnosis  AS [text()]  
                  From AbsDrgDiagnoses add1
                  Where add1.VisitID = add2.VisitID 
                  order by add1.VisitID,DiagnosisSeqID
                  For XML PATH ('')
                 ), 2, 1000) DiagText
  From [Livendb].[dbo].[AbsDrgDiagnoses] add2
) add3
on diag.VisitID = add3.VisitID 

Let me assume that when you remove it, the query is fast.

I think you would be better off with outer apply :

outer apply
    (select stuff((Select ', ' + add1.Diagnosis as [text()]  
                   From AbsDrgDiagnoses add
                   Where diag.VisitID = add.VisitID 
                   order by DiagnosisSeqID
                   For XML PATH ('')
                  ), 1, 2, '') DiagText
    ) add3

I can't imagine that the second level of subqueries actually helps performance.

And, speaking of performance, you can use an index on AbsDrgDiagnoses(VisitID, DiagnosisSeqID, Diagnosis) .