mysql 基础总结

一，基于CMD操作

1.数据库文件夹：

create   database  db1;                  #创建数据库db1

　  drop      database  db1;　　　      #删除数据库db1

show    databases db1;             #查看文件db1

use   db1;                                 #切换到t1文件

2.数据表:

 建表： create table t1用户表(id int auto_increment primary key,num int)

 engine=innodb default charset=utf8;

 show  tables;                   #查看建的表

 清空表：        delete from t1;          #清除内容但id从清除的数字开始        truncate table t1        #清除内容但id从零开始

 select count(1) from t1;        查看表里多少数据

 select * from t1;               查看t1表里的内容

desc   t1;                      查看t1是否有自增

show create table t1 \G;        查看t1表如何创建的

3. 增 删 改 查

增

   insert into tb11(name,age) values(‘alex‘,12);

insert into tb11(name,age) values(‘alex‘,12),(‘root‘,18);

insert into tb12(name,age) select name,age from tb11;删   delete from tb12;   delete from tb12 where id !=2    delete from tb12 where id =2    delete from tb12 where id > 2    delete from tb12 where id >=2    delete from tb12 where id >=2 or name=‘alex‘

改   update tb12 set name=‘alex‘ where id>12 and name=‘xx‘   update tb12 set name=‘alex‘,age=19 where id>12 and name=‘xx‘查

select * from tb12;

select id,name from tb12;

select id,name from tb12 where id > 10 or name =‘xxx‘;

select id,name as cname from tb12 where id > 10 or name =‘xxx‘;

select name,age,11 from tb12;

其他：

      alter table t1 auto_increment=2;   从序号二开始插入内容

      select * from tb12 where id != 1      select * from tb12 where id in (1,5,12);   查看1,5,12      select * from tb12 where id not in (1,5,12);   查看除1,5,12以外的      select * from tb12 where id in (select id from tb11)  查看表里具体一列，*只能一列      select * from tb12 where id between 5 and 12; 区（闭）间固定，取5到12之间。

通配符：

select * from tb12 where name like "a%"      举例 assss    afffffffff   select * from tb12 where name like "a_"       举例 as     ad     ac

分页：

select * from tb12 limit 10;    查看前十条

select * from tb12 limit 0,10;    从0开始后面取10条      select * from tb12 limit 10,10;      select * from tb12 limit 20,10;

select * from tb12 limit 10 offset 20;

# page = input(‘请输入要查看的页码‘)      # page = int(page)      # (page-1) * 10      # select * from tb12 limit 0,10; 1       # select * from tb12 limit 10,10;2

排序：      select * from tb12 order by id desc; 大到小      select * from tb12 order by id asc;  小到大       select * from tb12 order by age desc,id desc;

取后10条数据      select * from tb12 order by id desc limit 10;

分组：

select count(id),max(id),part_id from userinfo5 group by part_id;

count      max      min      sum      avg

**** 如果对于聚合函数结果进行二次筛选时？必须使用having ****      select count(id),part_id from userinfo5 group by part_id having count(id) > 1;

select count(id),part_id from userinfo5 where id > 0 group by part_id having count(id) > 1;

连表操作：

select * from userinfo5,department5

select * from userinfo5,department5 where userinfo5.part_id = department5.id

select * from userinfo5 left join department5 on userinfo5.part_id = department5.id      select * from department5 left join userinfo5 on userinfo5.part_id = department5.id      # userinfo5左边全部显示

# select * from userinfo5 right join department5 on userinfo5.part_id = department5.id      # department5右边全部显示

select * from userinfo5 innder join department5 on userinfo5.part_id = department5.id      将出现null时一行隐藏

select * from          department5       left join userinfo5 on userinfo5.part_id = department5.id      left join userinfo6 on userinfo5.part_id = department5.id

select          score.sid,         student.sid          from       score

left join student on score.student_id = student.sid

left join course on score.course_id = course.cid

left join class on student.class_id = class.cid

left join teacher on course.teacher_id=teacher.tid

select count(id) from userinfo5;