每天10句SQL（1）

1. 
   select max(grade) as 最高成绩 ,min(grade)as 最低成绩 
   from student_course
   where grade<90
-----------------------------------------------------------------------------------
2. 
   select sum(grade) from student_course 
-----------------------------------------------------------------------------------
3. 
   select count(*),count(student_id) from student
-----------------------------------------------------------------------------------
4. 
   select * from student_course
   where grade>60
   order by grade desc 
-----------------------------------------------------------------------------------
5. 
   select * from student_course
   where grade in('90' ,'98')
-----------------------------------------------------------------------------------
6. 
   select * from student_course
   where grade >60 and grade<80
   order by grade asc
-----------------------------------------------------------------------------------
   select * from student_course
   where grade between 60 and 80
   order by grade asc
-----------------------------------------------------------------------------------   
   select * from student_course
   where (grade between 60 and 80)
      or (grade between 20 and 40)
   order by grade asc
-----------------------------------------------------------------------------------
7. 
   select grade, count(*) from student_course
   where grade>60
   group by grade
-----------------------------------------------------------------------------------
8. 
   select grade, count(*) from student_course
   group by grade
   having count(*)>1
-----------------------------------------------------------------------------------
   select grade, count(*) from student_course
   group by grade
   having count(*)=1 or count(*)=3
-----------------------------------------------------------------------------------
   select grade, count(*) from student_course
   group by grade
   having count(*) in('1','3')
-----------------------------------------------------------------------------------
9. 
   select top 5 * from student_course
-----------------------------------------------------------------------------------
   select top 3 * from student_course
   where student_id not in ( select top 3 student_id from student_course 
   order by grade desc )
   order by grade desc
-----------------------------------------------------------------------------------
10. 
   select course_id from student_course 
-----------------------------------------------------------------------------------
   select distinct course_id from student_course 
-----------------------------------------------------------------------------------
   select distinct course_id ,student_id from student_course