Oracle常用语句

--如何用grade表的资料去更新usertable表的资料（有关联的字段userid）
 update usertable u set u.grade =
 (select g.grade from grade g where g.userid = u.userid);
 
--如何使查询结果字段生成序号
select rownum, t.* from sm_t_pad_new t
--如何快速做一个和原表一样的备份表
 create table new_table as (select * from user);
--如何查看数据文件的存放路径
select tablespace_name, file_id, bytes/1024/1024, file_name
from dba_data_files order by file_id;
--查询姓名相同的员工的信息
select u1.userid, u1.username from user u1,
(select username, count(*) from user group by username having count(username) > 1) u2
where u1.username = u2.username;
--根据时间查询
select * from user
where create_time >= to_date('2010-4-16 00:00:00','YYYY-MM-DD HH24:mi:ss')
and create_time <= to_date('2010-4-16 12:00:00','YYYY-MM-DD HH24:mi:ss')