Variable in Query

Hi

In one of my query I want to calulate the values based on price in material master (standard price & moving average price). I am getting these values in query using replacement path variables. Problem is that user want a selection for this price. If the user select std. price report should work on that otherwise it will be on moving average price.

How can I create a variable like that and get it calculated in a single query? If anybody have some idea pls reply.

Thanks

EV