Crystal Reports - SQL(urgent)

Question

Hello all, I am new to .net. I have a project which needs only reports to be created as a part of requirements. Hence, i have choosen asp .net c# and using Crystal Reports(CR). I have found CR's easy when the data is coming from one table. But, when it comes to multiple tables(like, selecting a column from a table and the result of this query would be an input to another SQL statement[nested SELECT statements]), it's kind of a becoming a problem to me. CR is creating the SQL statements by itself. I need to make changes to that SQL statement. How can i do it ? Can anyone help me with this problem. It's very urgent. All the suggestions are well accepted. Thanks everyone in advance. Please help! -Jos