Where and having

Select deptno, sum (SAL) from EMP where SAL> 1200 group by deptno having sum (SAL)> 8500 order by deptno;

1. A where clause and having clause can exist in an SQL statement: the WHERE clause filters data before grouping, and the condition cannot contain the aggregate function (sum (), AVG (), etc.); The having clause is used to filter data after a group. conditions often contain clustering functions.
2. The group by principle is that all columns not using aggregate functions after select must appear in the group by clause. If an order by clause exists, the clause after order by is placed at the end of the entire SQL statement.