摘要：select * from emp natural join dept order by DEPTNO DESC ; --自然查询 natural join 可以自己识别出两表中 相同的字段进行关联。select * from emp e,dept d where e.deptno=d.deptno 阅读全文

摘要：select sysdate from dual;select round(sysdate - hiredate) from emp; select * from emp; select round(1.8) from dual; --round 四舍五入select trunc(1.8) from 阅读全文