Techniques for optimizing queries are provided. In one technique, a query optimizer determines that two tables involved in equi-joins with one other table return unique rows. The query optimizer further determines that the rows returned by one of the tables is a subset of the rows returned by the other table. The query optimizer then determines that one of the two tables involved in the equi-joins can be eliminated. In another technique, a query optimizer determines that group-by placement may be used on a query that specifies a table. The query optimizer further determines that a view that (1) replaces the table and (2) results from the group-by placement is a subset of an existing view. The query optimizer further determines that each view is unique. The query optimizer selects an execution plan that does not join any tables or views with the resulting view or with the specified table.