union带有orderby的sql时，orderby需要放到子查询语法才有效

--union和order by连用需要放在子查询中，否则会报错
--例如：
--错误写法：
select * from dept1 order by deptno
union
select * from dept2 order by deptno;
--ORA-00933 "SQL command not properly ended"
--正确写法：
select * from (select * from dept1 order by deptno)
union
select * from (select * from dept2 order by deptno);