ADO.NET Parameter causes a timeout

Question

I have a big nasty pivot query that I run from C# via ADO.NET. I use this in 2 places and in 1 place I want the data but in the other place I just want the structure (no data). So in the query I added in the where clause:

1 = @test

So in the query where I only want the table structure I set @test to 2 and that works great. However, in the query I want the data I set it to 1 but that query times out then (after 5 mins). If I pull the sql into sql server and manually set the parameter it comes back in 3 mins. If I remove the 1 = @test completely from my C# app it comes back in 3 mins just fine. If I hardcode 1 = 1 in my C# app it comes back in 3 mins just fine.

I'm also adding a date parameter in this query and that works just fine.

My question is, what in the world about the @test parameter could cause this timeout from happening?

Is there a way to see what ADO.NET is really sending over to SQL Server for my query?

Answer 1

Simple answer is to modify the actual query when you need to do a structure only so that it contains your 1=@test. That way two separate query plans will be created, one for each type of query, both of which will be optimized best for the query it actually needs to do.