1、MySQL中利用视图可实现对子查询结果集的重复利用：
drop view if exists ali;
create view ali as (select * from deal);
select ali.Volume from ali;
2、SQLServer中利用With as可实现对子查询结果集的重复利用；
with summary as(
select dname,sum(sal) as dept_total from emp,dept where emp.deptno =dept.deptno group by dname
)
select dname,dept_total from summary where dept_total>(select sum(dept_total)*1/3 from summary)
3、PostgreSQL 中，也是创建视图以重复利用：
CREATE VIEW current_employees AS
SELECT NAME, ID, SALARY