SQL Reference

If GROUP BY or HAVING is used

• An expression X (not a column function) used in the select list must have a GROUP BY clause with:
  • a grouping-expression in which each column-name unambiguously identifies a column of R (see group-by-clause) or
  • each column of R referenced in X as a separate grouping-expression.
• The select list is applied to each group of R, and the result contains as many rows as there are groups in R. When the select list is applied to a group of R, that group is the source of the arguments of the column functions in the select list.