>>Did you try something like:
>>

>>SELECT .. WHERE myField = MyPar or MyField LIKE myPar + '%'

>>
>>Was the speed better?
>
>No, this doesn't change anything. To support this parameterized approach in regards to performance issue, I will have to use the text indexation as described by Rick. When I do it by putting the value as is in the SQL, it is an immediate result. So, because everything is parameterized, in order to avoid this downsize effect, I will look into the text indexation.

I'm not sure what you mean by parameterized. You mean use a named parameter for the Like value?

There should only be a tiny performance hit compared to static text and then only on the first hit as the query compiles. THere's no reason that a prepared statement should be noticably slower than a static query.

Something else is going on in your query. Get out Profiler and capture both queries then stick it into Query Analyzer and compare the execution plans.