oracle列别名使用

给列取一个其他名字，方便自己认识

select t.empno, t.ename from scott.emp t;

select t.empno, t.ename as 名字 from scott.emp t;
列名上显示名字两个字

给临时结果取名字

select t.deptno, count(*) from scott.emp t group by t.deptno;

select t.deptno, count(*) as total from scott.emp t group by t.deptno;

给临时结果用于嵌套查询使用

经典的分页查询

select * from (select t.*, rownum as rn from scott.emp t where rownum < 6) t where t.rn > 3