单表查询理论实践(三)
rade>=x and grade<=y
select *
from SC
where Grade between 90 and 80
--查询年龄在18岁以上女生，或者年龄不限的男生
select *
from Student
where (Ssex='女' and Sage>18) or Ssex = '男'
--查询 在IS系或者在MA系的学生
select *
from Student
where Sdept = 'IS' or Sdept = 'MA'
select *
from Student
where sdept in ('IS','MA')
--查询选修了3分以上课程的学生学号(使用不相关子查询，嵌套)
select distinct sno
from SC
where Cno in(
select Cno
from Course
where Ccredit>3
)
--查询3分以上课程的课程号和课程名，学分
select cno,cname,ccredit
from Course
where Ccredit>3
select * from Student
--查询3号课程的选修情况，结果按照成绩降序排列
select *
from SC
where Cno = '3'
order by Grade desc
--注意：desc降序，默认；asc是升序。
--查询，每个学生选修的课程平均分（分组统计）