Sql Server 数据库 多表连接操作

--相对应的数据库文件在下面

--多表连接查询

select Student.StudentName,Subject.SubjectName,Result.StudentResult from Student,Subject,Result

where Student.StudentNo=Result.StudentNo

and Subject.SubjectId=Result.SubjectId

order by StudentName

--inner join 链接的表必须有相同的列，主外键关系

select Student.StudentName,Subject.SubjectName,Result.StudentResult,Grade.GradeName,AVG(Result.StudentResult) as '平均分' from Student

inner join Subject

on Student.GradeId=Subject.GradeId

inner join Result

on Subject.SubjectId=Result.SubjectId

inner join Grade

on Grade.GradeId=Student.GradeId

where Grade.GradeName='s2'

group by Student.StudentName,Grade.GradeName,Subject.SubjectName,Result.StudentResult

having AVG(Result.StudentResult)>60

order by AVG(Result.StudentResult) desc

--查询年纪编号为1的年纪名称、科目名称及学时

select Grade.GradeName,Subject.SubjectName,Subject.ClassHour from Grade

inner join Subject

on Grade.GradeId=Subject.GradeId

where Grade.GradeId=1

--查询学生学号、姓名、考试科目及成绩

select Student.StudentNo,Student.StudentName,Subject.SubjectName,Result.StudentResult from Student

inner join Subject

on Student.GradeId=Subject.GradeId

inner join Result

on Result.SubjectId=Subject.SubjectId

--查询参加‘走进java编程世界’考试的学生姓名、成绩、日期

select Subject.SubjectName,Student.StudentName,Result.StudentResult,Result.ExamDate from Student

inner join Result

on Student.StudentNo=Result.StudentNo

inner join Subject

on Subject.SubjectId=Result.SubjectId

where Subject.SubjectName='走进Java编程世界'

order by Result.StudentResult desc

--左右连接

--左连接，左表和右表有数据差异，查出左表数据，右表差异部分显示为空

select distinct(Student.StudentNo),Result.SubjectId,Result.SubjectId from Student

 left join Result

 on Student.StudentNo=Result.StudentNo

 where Result.SubjectId is null

 --查询所有科目的参加考试的学生信息

 select * from Student

 left join Subject

 on Student.GradeId=Subject.GradeId

 --右连接的左边为右表连接数据

  --查询从未考试的科目信息

 select * from Result

right join Student

 on Student.StudentNo=Result.StudentNo

 where Result.StudentResult is null

 --查询所有年级对应的学生信息

 select * from Grade

 left join Student

 on Grade.GradeId=Student.GradeId