--创建数据库
create database studentsDB
--创建表
create table student
(
id int primary key,
stuid char(10),
stuname char(20),
classname char(20),
addresss char(40),
cols int,
sex char(10)
)
--更改数据项的数据类型
alter table student
alter column cols float
--插入数据
insert into student(id,stuid,stuname,classname,addresss,cols,sex)
values(1,'001','张三','1','重庆',100,'男')
insert into student(id,stuid,stuname,classname,addresss,cols,sex)
values(2,'002','李四','2','四川',70,'女')
insert into student(id,stuid,stuname,classname,addresss,cols,sex)
values(3,'003','李丽','1','贵州',99,'男')
insert into student(id,stuid,stuname,classname,addresss,cols,sex)
values(4,'004','王五','3','武汉',55,'女')
insert into student(id,stuid,stuname,classname,addresss,cols,sex)
values(5,'005','陈好','1','香港',67,'男')
--查询分数在60-100的信息
select id,stuid,stuname,classname,addresss,cols,sex from student where cols between 60 and 100
--查询班级里姓李的同学的信息
select id,stuid,stuname,classname,addresss,cols,sex from student where stuname like '李%'
--查询分数等于99和100的同学的信息
select id,stuid,stuname,classname,addresss,cols,sex from student where cols = 99 or cols =100
--根据分数降序排列
select id,stuid,stuname,classname,addresss,cols,sex from student order by cols desc
--根据性别求出男生和女生分数的平均值
select avg(cols) as 平均成绩,sex from student group by sex
--求出各班的平均成绩
select avg(cols) as 平均成绩,classname from student group by classname
