Question

I have a very simple query that is driving me absolutely nuts.

Here’s the situation:

• I have two database servers.
• One is an old SQL Server 2000 (VM), very minimal resources.
• The other is a very large SQL Server 2005 enterprise cluster with an absolutely ridiculous amount of resources available.
• I have a small portion of a larger query that executes in 3 seconds and returns 50,000+ rows of data on SQL Server 2000
• This same small query takes upwards of 15 minutes to return 1000 rows on SQL Server 2005
• The database I’m working with is a mirror image on these two servers. Same tables, same data in tables, same indexes on tables, etc.

I’ve tried creating different indexes on the SQL Server 2005 tables, defragged all the indexes that exist, updated table statistics, etc. Nothing has been able to make this query run faster on SQL Server 2005. Currently nothing else is running against the SQL Server 2005 server, and our DBAs assure me it’s not a configuration issue or anything to do with feature deprecation between SQL Server 2000 and SQL Server 2005.

The query is below:

SELECT (CASE 
             WHEN TeamMember.ID IN  (SELECT DISTINCT ProjMgrID FROM ProjMgr)
                THEN 'Yes' 
                ELSE 'No' 
        END) AS OnProjAsMgr 
FROM TeamMember

So return a distinct list of all the ProjMgrs, and if the TeamMember is on that list then assign “Yes” to the OnProjAsMgr value.

I’m a total SQL newbie, and this is code written by a predecessor. I don’t know if there’s a better way to write it, but I cannot figure out why it runs great on SQL Server 2000 but completely implodes on SQL Server 2005.

Answer 1

DISTINCT causes a sort, and IN causes the entire query to be evaluated. How does this version work:

SELECT OnProjAsMgr = CASE WHEN EXISTS 
  (SELECT 1 FROM dbo.ProjMgr WHERE ProjMgrID = TeamMember.ID)
  THEN 'Yes' 
  ELSE 'No' 
  END
FROM dbo.TeamMember;

If that fares no better then I suspect indexes are missing and no query will perform well without them.