You need to study the purpose and effects of the SQL WHERE clause for one of those problems. For the other, you should investigate what GROUP BY and DISTINCT do. The way to learn the subject matter is to try doing it, before and after studying. If you have specific questions about why some query you wrote does not yield the results you expect, folks here are likely to help. However, many or most are adverse to doing homework for students who appear too lazy to make a serious effort to do it themselves.