A GROUP BY clause, part of a SelectExpression, groups a result into subsets that have matching values for one or more columns. In each group, no two rows have the same value for the grouping column or columns. NULLs are considered equivalent for grouping purposes.
You typically use a GROUP BY clause in conjunction with an aggregate expression.
GROUP BY column-Name [ , column-Name ] *
column-Name must be a column from the current scope of the query; there can be no columns from a query block outside the current scope. For example, if a GROUP BY clause is in a subquery, it cannot refer to columns in the outer query.
SelectItems in the SelectExpression with a GROUP BY clause must contain only aggregates or grouping columns.
-- find the average flying_times of flights grouped by -- airport SELECT AVG (flying_time), orig_airport FROM Flights GROUP BY orig_airport SELECT MAX(city), region FROM Cities, Countries WHERE Cities.country_ISO_code = Countries.country_ISO_code GROUP BY region -- group by an a smallint SELECT ID, AVG(SALARY) FROM SAMP.STAFF GROUP BY ID -- Get the AVGSALARY and EMPCOUNT columns, and the DEPTNO column using the AS clause -- And group by the WORKDEPT column using the correlation name OTHERS SELECT OTHERS.WORKDEPT AS DEPTNO, AVG(OTHERS.SALARY) AS AVGSALARY, COUNT(*) AS EMPCOUNT FROM SAMP.EMPLOYEE OTHERS GROUP BY OTHERS.WORKDEPT;