primary key 维一键 不为空       autoinc 自动增长 在前面数自动加一

不加*搜什么就是什么 加*是所有信息

 

order by stuname asc  按名字升序排列   desc 降序

 

创建数据表

create table class

(

   cid  integer  primary key  autoincrement    ,

   cname varchar(20)

)

查询语句

select * from class

增加语句

insert into class (cname) values('IOS实训班')

修改语句

update class set cname='物联网'  where cid=2

删除语句

delete from class where cid=2

查询表中的记录数

select count(*) from class

select count(*) from class where cname='数据库'

select * from class where cname='数据库'

select cid from class where cname='数据库'

select cid,cname from class where cname='数据库'

select cid,cname from class where cid>=5 and cid<=9

select cid,cname from class where cid   between 5 and 9

select cid,cname from class where cid   in(5,6,7,8,9)

降序排列

select * from class  order by cid  desc

升序排列

select * from class  order by cid   asc

select * from class  where cname='数据库'  order by cid  desc

select * from class  where cname like  '%库'  order by cid  desc

select * from class  where cname like  '数_库'  order by cid  desc

分组

select count(*) from class group by cname

select count(*)   count  from class group by cname  order by count desc