Dear Svein and Dimitry,
thank you for both of your answers! That's really interesting.

I am in a quite hurry right now. Svein, I Like your approach and I will give it a try next week! The complete SP is about 500 lines for the query because it contains business rules interms of dates and rates of exchange. In the back are ten times more data than the 700 cases in about 10 - 15 tables.

Dimitry, why is it so that for every outer join the inner part is always re-evaluated?
And if I switch to an inner join, this could be avoided?

Thanks again!
Christian