mysql的相关用法

select * from student;
--删除studen 表中的数据；
delete from student where sno = 1234;
--删除student表
drop table student;
create table clazz(
        cno int(3) primary key,
        cname varchar(20) not null,
        croom int(3)
);
create table student(
        sno int(4),
        sname varchar(12) not null,
        gender char(3) default '男' check (gender in('男','女')),
        age int (3),
        sdate date,
        email varchar(50),
        cno int(3),
        constraint pk_student primary key(sno),
        constraint uk_student_email unique(email), 
        constraint ck_student_age check (age between 18 and 30),
        constraint fk_student_con foreign key (cno) references clazz(cno)
);
insert into clazz values(101, 'java大数据', 505);
insert into clazz values(102, 'UI设计', 311);
insert into clazz values(103, '人工智能', 520);

insert into student values(1234,'小明','男',19,sysdate(),'ming@sxt.com',101);
insert into student values(1235,'小红','女',18,now(),'hong@sxt.com',102);

select * from clazz;
select * from student;

--查询所有班级信息
select c.*,count(s.sno) cnt
from clazz c
left join student s
on c.cno=s.cno
group by c.cno,c.cname,c.croom
order by c.cno;

--分页
select * from clazz limit 0,2;
select * from clazz limit 2,2;
--当前页数，page
--每页显示的记录数，size
select * from clazz limit(page-1)*size,size;