Wow, this is quite a discussion, but i am having the impression we are missing the point here.
You have this where clause:
WHERE zzcostl = wa_sakto
I assume you have created an index containing this column. I hope you have a good amount of distinct values on it then in 99% of all cases the index will be picked automatically for the access path. Only in very rare case you would need to consider hints and stuff.
Cheers Michael