The Group By clause specifies the names of one or more columns by which the returned values are grouped. This clause is used to return a set of aggregate values.
Grammar
GROUP BY column_expression[,...]
where:
column_expression
is either a column name or a SQL expression. Multiple values must be separated by a comma. If column_expression is a column name, it must match one of the column names specified in the Select clause. Also, the Group By clause must include all non-aggregate columns specified in the Select list.
Example
The following example totals 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.
