数据库的增删改查

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