六、mysql数据库

1.查看当前所有数据库：show databases;

2.新建、删除数据库：create database qfdb；drop database qfdb;

3.使用某个数据库:use qfdb;

4.创建视图：create [or replace]view view_name[(column_list)] as select_statement

create view user_v(id,name,sex) as select id,name,sex from user;

5.查看创建视图的元数据 show create view user_v;

6.修改视图：alter view view_name[(column_list)]as select_statement

7.删除视图：drop view view_name

8.采用select语句将所选择的行直接写入到下个外部文件中去：select column_name into outfile filename

9.使用多条件进行多表查询：select a.username,a.sex,b.salary from userinfo a,usersalary b where a.userid=b.userid and b.salary>2000

10.使用分组排序查询：seletct a.sex,count(*) as count,avg(b.salary) from userinfo a,usersalary b where a.userid=b.userid and b.salary>2000 and b.salary<4000 group by a.sex