实验六 带函数查询和综合查询（1）

一、实验目的
1．掌握Management Studio的使用。
2．掌握带函数查询和综合查询的使用。

二、实验内容及要求
1统计年龄大于30岁的学生的人数。

select count(*)
from student
where year(getdate())-year(birthday)>30

2统计数据结构有多少人80分或以上。

select count(*)
from studentgrade,course
where course_name='数据结构' 
and course.course_id=studentgrade.course_id
and grade>=80

3 查询“0203”课程的最高分的学生的学号。（请分别用TOP1和函数来进行查询，并分析它们的区别）

方法一
select stu_id
from studentgrade
where grade=(
            select max(grade)
            from studentgrade
            where course_id='0203')
      and course_id='0203'
方法二
select top 1 stu_id
from studentgrade
where course_id='0203'
order by grade desc

4 统计各系开设班级的数目(系名称、班级数目)，并创建结果表。（需考虑没有班级的系）

select depar_name,count(class_id) as 班级数目
into newtable1
from deparment left outer join class on(deparment.depar_id=class.depar_id)
group by depar_name

5 选修了以“01”开头的课程的学生学号，姓名，选课的课程号。

select student.stu_id,stu_name,course_id
from student,studentgrade
where course_id like '01%'
 and student.stu_id=studentgrade.stu_id

6 统计每科目的最高分、最低分，平均分、总分，并以中文列名显示。

select course_name 课程,max(grade) 最高分,min(grade) 最低分,avg(grade) 平均分,sum(grade) 总分
from studentgrade,course
where studentgrade.course_id=course.course_id
group by course_name

7 所有成绩都在70分以上的学生姓名（提示：使用子查询。需考虑未选课的学生）

方法一：连接查询(group by student.stu_id不能省略stu_id,否则同名的“涂杰杰”只出现一次）
select student.stu_id,stu_name  /*student.stu_id可省略*/
from student,studentgrade
where student.stu_id=studentgrade.stu_id
group by student.stu_id,stu_name   
having min(grade)>=70

方法二：嵌套查询
select stu_id,stu_name
from student
where stu_id in(select stu_id 
                from studentgrade
                group by stu_id
                having min(grade)>=70)

select student.stu_id,stu_name,grade
from student,studentgrade
where student.stu_id=studentgrade.stu_id

8 “数据库”课程得最高分的学生的姓名、性别和所在系（提示：使用子查询）

方法一：/*top 1只能显示第一个最高分，不正确*/
select top 1 stu_name, stu_sex,depar_name
from student,deparment,class,course,studentgrade
where deparment.depar_id=class.depar_id
   and class.class_id=student.class_id
   and student.stu_id=studentgrade.stu_id
   and studentgrade.course_id=course.course_id
   and course_name='数据库' 
   order by grade desc

方法二：/*top 1只能显示第一个最高分，不正确*/
select stu_name, stu_sex,depar_name
from student,deparment,class
where deparment.depar_id=class.depar_id
   and class.class_id=student.class_id
   and stu_id=(select top 1 stu_id
               from studentgrade
               where course_id=(select course_id 
                                from course
                                where course_name='数据库' )
               order by grade desc)

方法3：
select student.stu_id,stu_name, stu_sex,depar_name
from student,deparment,class,studentgrade
where deparment.depar_id=class.depar_id
   and class.class_id=student.class_id
   and student.stu_id=studentgrade.stu_id 
  and grade= (select max(grade) 
            from studentgrade
            where course_id=(select course_id 
                                from course
                                where course_name='数据库' )
               )
/*错误，不是数据库的最高分，如果和数据库的最高分相同的人也会出现，为什么？*/


select student.stu_id,stu_name, stu_sex,depar_name
from student,deparment,class,studentgrade,course
where deparment.depar_id=class.depar_id
   and class.class_id=student.class_id
   and student.stu_id=studentgrade.stu_id 
  and course.course_id=studentgrade.course_id
and grade= (select max(grade) 
            from studentgrade
            where course_id=(select course_id 
                                from course
                                where course_name='数据库' )
               )
and course_name='数据库'
方法 4:
select student.stu_id,stu_name, stu_sex,depar_name
from student,deparment,class,studentgrade,course
where deparment.depar_id=class.depar_id
   and class.class_id=student.class_id
   and student.stu_id=studentgrade.stu_id 
  and course.course_id=studentgrade.course_id
and grade= (select max(grade) 
            from studentgrade,course
            where studentgrade.course_id=course.course_id
                and course_name='数据库' 
               )
and course_name='数据库'

9 至少选修了两门课及以上的学生姓名和性别

select stu_name,stu_sex
from student
where stu_id in (select stu_id
              from studentgrade
              group by stu_id
              having count(*)>=2)