Originally posted by jzhu
If you use distinct, it should not return duplicates. It would be helpful if you give us your query.
A couple of things come to mind.
1) Is the data clean? Dup records could cause a problem.
2) Take a close look at your joins, you could be receiving a cartesian product.
3) If the joins are correct the problem may be in the WHERE criteria. When joining many tables, especially where 1 to many relationships exists, its possible your WHERE clause is not specific enough to bring the number of returns down to a single row.