【Sql】sql语句练习随记

news2024/11/17 6:55:08

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。

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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');