6继续玩，改变查询结果列名

select name as xm,birthday as workday from student;--修改列名name为xm，birthday为workday

select * from student;

7 select xh||sex from student--将选择的字段竖行排列

8 select name,sal,

case when sal<=10000 then 'underpaid'

     when sal>=30000 then 'overpaid'

       else 'ok'

      end as status

      from student--当大于30000，输出薪酬过高，小于10000输出过低，其他正常

10 select*from student where rownum<=5;--限制出现行数为五行¡