SQL查询在SSMS中花费的时间不到1秒，而在代码中花费的时间则永远

Question

I'm running this query against a quite big table (i guess, around 150-200 000 rows):

select count(Distinct(eti.Email)) FROM table1 eti 
LEFT OUTER JOIN table2 ti on ti.Email = eti.Email and ti.SiteId = eti.Site_Id 
WHERE eti.Site_Id=1

In SMMS (SQL Server Management Studio) it takes less than 1 secound to execute but when I try to execute from my ASP.NET-site it times out.

I'm using PetaPoco to fetch the data which "under the hood" executes this code:

using (var cmd = CreateCommand(_sharedConnection, sql, args))
{
    object val = cmd.ExecuteScalar();
    OnExecutedCommand(cmd);
    return (T)Convert.ChangeType(val, typeof(T));
}

I've been reading about that SSMS has som "special settings" when it executes the query? I really need to get this up and running.

Could the "MARS"-setting in the connection be have any impact on this? How do i debug and find the problem?

Thanks!

Answer 1

Thank you for the help!

I have finally found the issue (and it's a little embarrassing)... I found this blog question from msdn forums about sp_executesql being slow: and Dan Guzman who is SQL Server MVP answers: http://social.msdn.microsoft.com/Forums/en-US/transactsql/thread/3cb08860-49a0-432a-8605-0af6b374dded/

Another possible issue is data type mismatches between the parameters and the column data types, resulting in non-sargable expressions and a bad plan. Please post your query and table DDL if you need further help.

So i doubled checked and it turned out that table2 had both the Email and the SiteId-fields set as "Nullable", changing them to match table1 fixed the issue.