A technique relates to determining when to skip a group by clause in a query. A computer checks that a condition is satisfied for a table. The condition is selected from the group consisting of having a unique index on one or more columns of the table or having a function on the one or more columns that makes rows in the GROUP BY clause unique. The group by clause is part of the query on the table. In response to the condition being satisfied, the group by clause associated with the one or more columns is skipped. In response to the condition not being satisfied, the group by clause associated with the one or more columns is executed.