1.创建表
create table student(
sno int,
sname varchar(8),
ssex varchar(2),
sbirth datetime,
sstate bit
);
create table sex(
sexno int,
sexname varchar(2),
primary key (sexno)
);
create table grade(
sno int,
cno int,
scgrade float
primary key(sno,cno),
foreign key (sno) references student(sno),
foreign key (cno) references course(cno)
);
create table grade(
sno int,
cno int,
scgrade float
constraint pk_2 primary key(sno,cno),
constraint fk_1 foreign key (sno) references student(sno),
constraint fk_2 foreign key (cno) references course(cno)
);
create table course(
cno int primary key,
cname varchar(20)
);
2.修改表
alter table student alter column sno int not null;
alter table student alter column ssex int;
alter table student add constraint pk_1 primary key (sno);
alter table student drop constraint pk_1;
alter table course drop column cgrade;
alter table course add cname varchar(20) not null;
alter table course add cteacher varchar(4);
3.插入数据
insert into student values(1,'yuan',2,'1987-08-10',0);
insert into student values(2,'hui',2,'1987-08-10',0);
insert into student values(3,'xian',2,'1987-08-10',0);
insert into student values(4,'yang',1,'1986-10-17',0);
insert into student values(5,'feng',1,'1986-10-17',0);
insert into student values(6,'jiang',1,'1986-10-17',0);
insert into sex values(1,'男');
insert into sex values(2,'女');
insert into grade values(1,1,80);
insert into course values(1,'a','a');
insert into course values(2,'a','a');
insert into course values(3,'a','a');
insert into course values(4,'a','a');
insert into course values(5,'a','a');
insert into grade values(1,2,70);
insert into grade values(1,3,60);
insert into grade values(1,4,50);
insert into grade values(1,5,40);
insert into grade values(2,1,50);
4.删除表
drop table student;
drop table grade;
drop table course;
5.查询
select * from student;
6.删除数据
delete student;
7.时间函数datediff的应用
select sbirth,datediff(year,sbirth,getdate()) from student;
select day(sbirth)from student;
8.去除重复的行
select distinct ssex from student;
9.查询字段去除转义字符
where sname like 'hui\_xian' escape '\';
10.排序
select sname,sbirth from student
order by sname desc;
11.取查询结果中的部分数据top
select top 50 percent sname,sno,sbirth from student order by sname desc;
12.聚集函数的应用
select max(scgrade),avg(scgrade),min(scgrade) from grade
where sno=1;
13.GROUP BY的应用
Having子句用于对分组后的结果再进行过滤，它的功能有点像Where子句，但它用于
组而不是单个记录。在Having子句中可以使用聚集函数，但在Where子句中则不能。
Having通常与Group by子句一起使用。
select sno,count(cno) from grade
group by sno
having count(*)>2;