本文通过最经典的“学生-成绩-课程-教师”表来帮助练习sql语句。

STUDENT表

• SNO 学号
• SNAME 姓名
• SSEX 性别
• SBIRTHDAY 生日
• CLASS 班级

SCORE表

• SNO 学号
• CNO 课程编号
• DEGREE 分数

COURSE表

• CNO 课程编号
• CNAME 课程名称
• TNO 教师编号

TEACHER表

• TNO 教师编号
• TNAME 教师姓名
• TSEX 性别
• TBIRTHDAY 生日
• PROF 职称
• DEPART 系部

1. 查询“12”班学生所选各个课程的平均分。

select CNO, avg(DEGREE)
from SCORE
where SNO in (select SNO
              from STUDENT
              where CLASS = '12')
group by CNO

2. 查询和学号为108的同学同年出生的所有学生的Sno、Sname和Sbirthday列。

select
  SNO,
  SNAME,
  SBIRTHDAY
from STUDENT
where year(SBIRTHDAY) = (
  select year(SBIRTHDAY)
  from STUDENT
  where SNO = '108'
);

3. 查询“李明“教师任课的学生成绩。

select *
from SCORE
where CNO in (
  select CNO
  from COURSE
    inner join TEACHER on COURSE.TNO = TEACHER.TNO and TNAME = '李明'
);

4. 查询选修某课程的同学人数多于5人的教师姓名。

select TNAME
from TEACHER
where TNO in (
  select TNO
  from COURSE
  where CNO in (select CNO
               from SCORE
               group by CNO
               having count(SNO) > 5)
);

5. 查询“计算机系”中与“电子工程系“不同职称的教师的Tname和Prof。

select
  tname,
  prof
from TEACHER
where depart = '计算机系' and prof not in (
  select prof
  from TEACHER
  where depart = '电子工程系'
);

6. 查询所有教师和同学的name、sex和birthday。

select
  TNAME     name,
  TSEX      sex,
  TBIRTHDAY birthday
from TEACHER
union
select
  sname     name,
  SSEX      sex,
  SBIRTHDAY birthday
from STUDENT;

7. 查询成绩比该课程平均成绩低的同学的成绩表。

select * 
from score 
join (select CNO, avg(DEGREE) as avg from SCORE group by CNO) t1 
on score.sno = t1.cno 
where score.degree < t1.avg;

8. 查询所有未讲课教师的Tname和Depart。

select TNAME,DEPART
from teacher
where TNO not in (select distinct(TNO) from course);

9. 查询至少有2名男生的班号。

select class
from student
where SSEX = '男'
group by class
having count(SSEX)>1

10. 查询Student表中每个学生的姓名和年龄。

select
  SNAME,
  year(now()) - year(SBIRTHDAY)
from STUDENT;

11. 查询和“李军”同性别并同班的同学Sname。

select sname
from STUDENT
where (SSEX, CLASS) = (select
                         SSEX,
                         CLASS
                       from STUDENT
                       where SNAME = '李军');