The Group By clause specifies the names of one or more fields by which the returned values should be grouped. This clause is used to return a set of aggregate values. It has the following form:
GROUP BY column_expressions
column_expressions must match the column expression used in the Select clause. A column expression can be one or more field names of the database table, separated by a comma (,) or one or more expressions, separated by a comma (,). See SQL Expressions for details.
The following example sums the salaries in each department:
SELECT dept_id, sum(salary) FROM emp GROUP BY dept_id
This statement returns one row for each distinct department ID. Each row contains the department ID and the sum of the salaries of the employees in the department.
