Question

I’d like to know how I can increase the performance and efficiency of my SQL statement.
Does anyone have some ideas or advices?

DECLARE @RoleName NVARCHAR(MAX)
DECLARE @result INT

SELECT @result = COUNT(DurchlaufVorgang.Durchlaufname)
FROM   DurchlaufVorgang
INNER JOIN RoleDepartment
        ON DurchlaufVorgang.AbteilungID = RoleDepartment.ID
WHERE  DurchlaufVorgang.Depricated = 'FALSE'
       AND RoleDepartment.RoleName = @RoleName
       AND RoleDepartment.Depricated = 'FALSE'

SELECT Antraege.AntragID
FROM   ArtikelMitteilung,
       Antraege
WHERE  ArtikelMitteilung.Status = 'Opened'
       AND Antraege.AntragID NOT IN 
          (SELECT Antraege.AntragID
           FROM   Vorgang,
                  Antraege
           WHERE  Vorgang.StepID IN 
                  (SELECT DurchlaufVorgang.ID
                   FROM   DurchlaufVorgang
                   INNER JOIN RoleDepartment
                           ON DurchlaufVorgang.AbteilungID = RoleDepartment.ID
                   WHERE DurchlaufVorgang.Depricated = 'FALSE'
                     AND RoleDepartment.RoleName = @RoleName
                     AND RoleDepartment.Depricated = 'FALSE')
              AND Vorgang.AntragsID = Antraege.ID
            GROUP  BY Antraege.AntragID
            HAVING COUNT(Antraege.AntragID) >= @result)
       AND ArtikelMitteilung.AntragsID = Antraege.ID
GROUP  BY Antraege.AntragID  

I’m grateful for your help.

Answer 1

You’re not doing anything glaringly wrong in your query. The SQL optimizer will take a large statement like that and figure out the best way to execute it. Where you can run into problems is if your indices are fragmented or non-existent.

From SQL Server Management Studio, click on Show Execution Plan and see if it suggests any additional indices. De-fragment your indices (you can just drop and re-add them if you’re in a testing environment).

If your intuition is that a big statement is bad for performance, that should not be the case here. In fact, it should help the optimizer because it gives it more choices on how to execute it.