如有以下sql语句：
select name from student where id='1003' union all select name from student where id='1001' union all select name from student where id='1004'
查询出来的结果顺序是未知的。
现在必须按照一定的顺序显示查询的结果，可以用这样的方法：
select name from ( select name ,2 flag from student where id='1003' union all select name ,1 flag from student where id='1001' union all select name ,3 flag from student where id='1004') tem order by flag
