记录个Sql分组使用

话说好久没写Sql了，结果和其他小组的同事写Sql的时候遭到鄙视了，看来Sql是永远不能丢的，有时间就要温习一下。

创建3张表：

Rel_SutAndCourse，T_Course，T_Stu

为3张表填充数据：

----Student
begin transaction

insert T_Stu(StuCode,StuName,Sex) values (‘Stu001‘,‘zhang chu chu‘,1)
insert T_Stu(StuCode,StuName,Sex) values (‘Stu002‘,‘li xiao long‘,1)
insert T_Stu(StuCode,StuName,Sex) values (‘Stu003‘,‘cheng long‘,1)
insert T_Stu(StuCode,StuName,Sex) values (‘Stu004‘,‘liu shi shi‘,0)

insert T_Stu(StuCode,StuName,Sex) values (‘Stu005‘,‘yang mi‘,0)
insert T_Stu(StuCode,StuName,Sex) values (‘Stu006‘,‘a sa‘,0)
insert T_Stu(StuCode,StuName,Sex) values (‘Stu007‘,‘a jiao‘,0)

commit transaction

----Course
select * from T_Course
begin transaction

insert T_Course(CourseCode,CourseName) values (‘course01‘,‘yu wen‘)
insert T_Course(CourseCode,CourseName) values (‘course02‘,‘shu xue‘)
insert T_Course(CourseCode,CourseName) values (‘course03‘,‘ying yu‘)
insert T_Course(CourseCode,CourseName) values (‘course04‘,‘ti yu‘)

commit transaction

----Relation
select * from Rel_SutAndCourse

begin transaction

insert Rel_SutAndCourse(StuId,CourseId,CreateTime) values (1,1,GETDATE())
insert Rel_SutAndCourse(StuId,CourseId,CreateTime) values (2,1,GETDATE())
insert Rel_SutAndCourse(StuId,CourseId,CreateTime) values (3,2,GETDATE())
insert Rel_SutAndCourse(StuId,CourseId,CreateTime) values (3,3,GETDATE())

insert Rel_SutAndCourse(StuId,CourseId,CreateTime) values (4,1,GETDATE())
insert Rel_SutAndCourse(StuId,CourseId,CreateTime) values (4,2,GETDATE())
insert Rel_SutAndCourse(StuId,CourseId,CreateTime) values (4,3,GETDATE())
insert Rel_SutAndCourse(StuId,CourseId,CreateTime) values (4,4,GETDATE())
insert Rel_SutAndCourse(StuId,CourseId,CreateTime) values (3,1,GETDATE())

insert Rel_SutAndCourse(StuId,CourseId,CreateTime) values (5,1,GETDATE())
insert Rel_SutAndCourse(StuId,CourseId,CreateTime) values (6,1,GETDATE())
insert Rel_SutAndCourse(StuId,CourseId,CreateTime) values (7,1,GETDATE())

commit transaction

然后虚拟出3个需求：

--查询出每门课程选课的学生数
select CourseId,count(*) as SutCount from Rel_SutAndCourse
group by CourseId

--查询每个学生选的课的数目
select StuId,count(*) as SutCount from Rel_SutAndCourse
group by StuId

--查询男女同学选课的数量
select stu.sex,Count(distinct rel.stuid) from Rel_SutAndCourse rel
inner join T_Stu stu on rel.StuId=stu.Id
group by stu.sex

--以2014-08-03 19:55为时间分割点，查询哪些同学在时间点之前选课，哪些在时间点之后选了课
select * from Rel_SutAndCourse

select stu.Id,stu.StuName from T_Stu stu
join Rel_SutAndCourse rel on stu.id=rel.StuId
where rel.Id<=(
select max(rel.Id) from Rel_SutAndCourse rel
where rel.CreateTime<‘2014-08-03 19:55‘
) group by stu.Id,stu.StuName

select stu.Id,stu.StuName from T_Stu stu
join Rel_SutAndCourse rel on stu.id=rel.StuId
where rel.Id>=(
select min(rel.Id) from Rel_SutAndCourse rel
where rel.CreateTime>‘2014-08-03 19:55‘
) group by stu.Id,stu.StuName

其实就是个简单的分组，一直认为自己的Sql是写的最烂的，看来必须加强啊，争取每次学一些。

记录个Sql分组使用