View restrictions and advanced uses

Views can be thought of as computed tables. Any SELECT command can be used in a view definition except commands containing ORDER BY. Views can use GROUP BY clauses, subqueries, and joins. Disallowing ORDER BY is consistent with the fact that rows of a table in a relational database are not stored in any particular order. When you use the view, you can specify an ORDER BY.

You can also use views in more complicated queries. Here is an example using a join:

SELECT LastName, dept_head_id
FROM emp_dept, department
WHERE emp_dept.Department = department.dept_name