SQL笔试经典40题

目录

一、前言

SQL简介

SQL 分类

二、实践（50道SQL题）

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一、前言

SQL是我接触的第二门编程语言，学得挺早，但到现在已经好几年没用过SQL了，因为搞机器学习用python（numpy/pandas），最近刷笔试题遇到SQL题都有点忘了，故再次拾起，回顾回顾。本文所使用的数据库为Oracle19c。

SQL简介

SQL (Structured Query Language) 是具有数据操纵和数据定义等多种功能的数据库语言，这种语言具有交互性特点，能为用户提供极大的便利，数据库管理系统应充分利用SQL语言提高计算机应用系统的工作质量与效率。

• SQL 语句可以单行或多行书写，以分号结尾；
• 可以用空格和缩进来来增强语句的可读性；
• 关键字不区别大小写，建议使用大写；
• 单行注释用两条杠“--单行内容”，多行注释用“/* 多行内容 */”

SQL 分类

• DDL（Data Definition Language）：数据定义语言，用来定义数据库对象：库、表、列等。关键字：create创建、alter修改、drop删除、truncate清空
• DML（Data Manipulation Language）：数据操作语言，用来定义数据库记录（数据）。关键字：insert插入、update更新、delete删除
• DCL（Data Control Language）：数据控制语言，用来定义访问权限和安全级别。关键字：grant授权、revoke撤权
• DQL（Data Query Language）：数据查询语言，用来查询记录（数据）。关键字：select查询
• TCL（Transaction Control Language）：事务控制语言。关键字：commit提交、rollback回滚、savepoint保存点

二、实践（50道SQL题）

首先，建表，插入数据，以供后面的数据查询操作。

create table Student(sid varchar(10),sname varchar(10),sage varchar(10),ssex varchar(10));
insert into Student values('01' , '赵雷' , '1990-01-01' , '男');
insert into Student values('02' , '钱电' , '1990-12-21' , '男');
insert into Student values('03' , '孙风' , '1990-05-20' , '男');
insert into Student values('04' , '李云' , '1990-08-06' , '男');
insert into Student values('05' , '周梅' , '1991-12-01' , '女');
insert into Student values('06' , '吴兰' , '1992-03-01' , '女');
insert into Student values('07' , '郑竹' , '1989-07-01' , '女');
insert into Student values('08' , '王菊' , '1990-01-20' , '女');
create table Course(cid varchar(10),cname varchar(10),tid varchar(10));
insert into Course values('01' , '语文' , '02');
insert into Course values('02' , '数学' , '01');
insert into Course values('03' , '英语' , '03');
create table Teacher(tid varchar(10),tname varchar(10));
insert into Teacher values('01' , '张三');
insert into Teacher values('02' , '李四');
insert into Teacher values('03' , '王五');
create table SC(sid varchar(10),cid varchar(10),score number(18,1));
insert into SC values('01' , '01' , 80);
insert into SC values('01' , '02' , 90);
insert into SC values('01' , '03' , 99);
insert into SC values('02' , '01' , 70);
insert into SC values('02' , '02' , 60);
insert into SC values('02' , '03' , 80);
insert into SC values('03' , '01' , 80);
insert into SC values('03' , '02' , 80);
insert into SC values('03' , '03' , 80);
insert into SC values('04' , '01' , 50);
insert into SC values('04' , '02' , 30);
insert into SC values('04' , '03' , 20);
insert into SC values('05' , '01' , 76);
insert into SC values('05' , '02' , 87);
insert into SC values('06' , '01' , 31);
insert into SC values('06' , '03' , 34);
insert into SC values('07' , '02' , 89);
insert into SC values('07' , '03' , 98);

两张表的数据如下：

 

1、查询“01”课程比“02”课程成绩高的所有学生的学号

select distinct t1.sid as sid
from 
    (select * from sc where cid='01')t1
left join 
    (select * from sc where cid='02')t2
on t1.sid=t2.sid
where t1.score>t2.score;

2、查询平均成绩大于60分的同学的学号和平均成绩；

select 
    sid
    ,avg(score)
from sc
group by sid
having avg(score)>60;

3、查询所有同学的学号、姓名、选课数、总成绩

select
    student.sid as sid
    ,sname
    ,count(distinct cid) course_cnt
    ,sum(score) as total_score
from student
left join sc 
on student.sid=sc.sid
group by student.sid,sname;

4、查询姓“李”的老师的个数；

select
    count(distinct tid) as teacher_cnt
from teacher
where tname like '李%';

5、查询没学过“张三”老师课的同学的学号、姓名；

select sid,sname from student where sid not in (
select s.sid from sc s where cid in (
select c.cid from course c inner join teacher t on c.tid=t.tid where t.tname='张三'
));

6、查询学过“01”并且也学过编号“02”课程的同学的学号、姓名；

select sid,sname from student where sid in (
select sid from sc s1
where s1.cid = '01' and exists (select 1 from sc s2 where s2.cid = '02' and s1.sid = s2.sid)
);

7、查询学过“张三”老师所教的课的同学的学号、姓名

select sid,sname from student where sid in (
select sid from sc s inner join course c on s.cid=c.cid
inner join teacher t on c.tid = t.tid
where t.tname='张三'
);

8、查询课程编号“01”的成绩比课程编号“02”课程低的所有同学的学号、姓名；

select sid,sname from student where sid in(
select sid from sc s1 where s1.cid='01' and exists 
(select 1 from sc s2 where s1.sid=s2.sid and s2.cid='02' and s1.score<s2.score)
);

9、查询所有课程成绩小于60分的同学的学号、姓名；

--方法一：找分数表中分数大于60分的同学，排除这些人即可
select sid,sname from student where sid not in(
select sid from sc where score>=60)
and sid in (select sid from sc);

--方法二：分组
SELECT s.sid,s.sname
FROM student s
inner join (
	select sid from sc group by sid having max(score) < 60
) t on s.sid = t.sid

10、查询没有学全所有课的同学的学号、姓名；

select sid,sname from student where sid not in(
select sid from sc group by sid 
having count(distinct cid)=(select count(distinct cid) from course));

11、查询至少有一门课与学号为“01”的同学所学相同的同学的学号和姓名；

select sid,sname from student where sid in(
select distinct sid from sc s1 where sid !='01' and exists
(select 1 from sc s2 where sid ='01' and s1.cid=s2.cid)
);

12、查询和"01"号的同学学习的课程完全相同的其他同学的学号和姓名

select sid,sname from student where sid in (
select s.sid from sc s inner join 
(select distinct cid from sc where sid='01') x on s.cid=x.cid
group by s.sid having count(distinct s.cid)=(select count(distinct cid) from  sc where sid='01')
) and sid!='01';

13、把“SC”表中“张三”老师教的课的成绩都更改为此课程的平均成绩；

update sc
set score=
(
  select avg_score from 
  (
    select avg(score) avg_score
    from sc s
    inner join course c on s.cid = c.cid
    inner join teacher t on c.tid = t.tid
    where t.tname = '张三'
  ) x
) 
where cid in(
    select distinct s.cid from sc s
    inner join course c on s.cid = c.cid
    inner join teacher t on c.tid = t.tid
    where t.tname = '张三'
);

14、查询没学过"张三"老师讲授的任一门课程的学生姓名

select sid,sname from student
where sid not in (
select sid from sc s
inner join course c on s.cid=c.cid
inner join teacher t on c.tid=t.tid
where t.tname='张三');

15、查询两门及其以上不及格课程的同学的学号，姓名及其平均成绩

select t.sid,t.sname,s.avg_score from student t inner join 
(
select sid,avg(score) avg_score 
from sc 
where score<60 
group by sid 
having count(distinct cid)>=2
) s on t.sid=s.sid;

16、检索"01"课程分数小于60，按分数降序排列的学生信息

select t.sid,t.sname,s.score from sc s
inner join student t on s.sid=t.sid
where s.cid='01' and s.score<60 
order by score desc

17、按平均成绩从高到低显示所有学生的平均成绩

select t.sid,t.sname,s.avg_score from student t
inner join 
(select sid,avg(score) avg_score
from sc group by sid ) s 
on t.sid=s.sid
order by avg_score desc;

18、查询各科成绩最高分、最低分和平均分：以如下形式显示：课程ID，课程name，最高分，最低分，平均分，及格率

select c.cid,c.cname,max(s.score) max_score,min(s.score) min_score,avg(s.score) avg_score,
sum(case when score>=60 then 1 end)/count(1) pass_ratio
from sc s
inner join course c on s.cid=c.cid
group by c.cid,c.cname;

19、按各科平均成绩从低到高和及格率的百分数从高到低顺序

select cid,avg(score) avg_score,
sum(case when score>=60 then 1 end)/count(1) pass_ratio
from sc 
group by cid
order by avg_score,pass_ratio desc;

20、查询学生的总成绩并进行排名

select sid,sum(score) sum_score ,
rank() over(order by sum(score) desc) rank
from sc
group by sid;

21、查询不同老师所教不同课程平均分从高到低显示

select t.tname,c.cname,avg(s.score) avg_score
from course c inner join teacher t on c.tid = t.tid
inner join sc s on c.cid=s.cid
group by t.tname,c.cname
order by avg_score desc;

22、查询所有课程的成绩第2名到第3名的学生信息及该课程成绩

select sid,cid,score,r
from (
select s.*,dense_rank() over(partition by cid order by score desc) r
from sc s
) m where r=2 or r=3;

23、统计各科成绩各分数段人数：课程编号,课程名称,[100-85],[85-70],[70-60],[0-60]及所占百分比

select c.cid,c.cname,
sum(case when s.score>=85 then 1 else 0 end)/count(1) between85to100,
sum(case when s.score>=70 and s.score<85 then 1 else 0 end)/count(1)  between70to85,
sum(case when (s.score>=60 and s.score<70) then 1 else 0 end)/count(1) between60to70,
sum(case when (s.score<60) then 1 else 0 end)/count(1) between0to60
from sc s
inner join course c on s.cid=c.cid
group by c.cid,c.cname;

24、查询学生平均成绩及其名次

select sid,avg(score) avg_score
,row_number() over (order by avg(score) desc) AS rank
from sc
group by sid;

25、查询各科成绩前三名的记录

select cid,sid,score,rank from
(
  select s.*,rank() over (partition by cid order by score desc) rank
  from sc s
) t
where t.rank<=3;

26、查询每门课程被选修的学生数

select cid,count(distinct sid) cnt
from sc
group by cid;

27、查询出只选修了两门课程的全部学生的学号和姓名

select s.sid,s.sname 
from sc
left join student s on sc.sid = s.sid 
group by s.sid,s.sname 
having count(distinct cid)=2;

28、查询男生、女生人数

--方法一
select 
  sum(decode(ssex,'男',1,0)) AS 男生人数
  ,sum(decode(ssex,'女',1,0)) AS 女生人数
from student;

--方法二
select ssex,count(ssex) 
from student
group by ssex;

29、查询名字中含有"风"字的学生信息

select *
from student
where sname LIKE '%风%'

30、查询同名同性学生名单，并统计同名人数

select sname ,count(sname) cnt 
from student 
group by sname 
having count(sname)>=2;

31、查询1990年出生的学生名单

select *
from student 
where substr(sage,1,4)='1990';

32、查询每门课程的平均成绩，结果按平均成绩升序排列，平均成绩相同时，按课程号降序排列

select
    cid,avg(score) as avg_score
from sc
group by cid
order by avg_score,cid desc

33、查询不及格的课程，并按课程号从大到小排列

select
    cid,sid,score
from sc
where score<60
order by cid desc,sid;

34、查询课程编号为"01"且课程成绩在60分以上的学生的学号和姓名；

select sid,cid,score
from sc
where cid='01' and score>60;

35、查询选修“张三”老师所授课程的学生中，成绩最高的学生姓名及其成绩

select * from (
select sc.sid,sname,cname,score
from sc
left join course
    on sc.cid=course.cid
left join teacher
    on course.tid=teacher.tid
left join student
    on sc.sid=student.sid
where tname='张三'
order by score desc
) m where rownum<=1;

36、统计每门课程的学生选修人数（超过5人的课程才统计）。要求输出课程号和选修人数，查询结果按人数降序排列，若人数相同，按课程号升序排列

select
    cid
    ,count(sid) cnt
from sc
group by cid
having count(sid)>=5
order by cnt desc,cid;

37、检索至少选修两门课程的学生学号

select
    sid
    ,count(cid)
from sc
group by sid
having count(cid)>=2;

38、查询各学生的年龄

select (sysdate-to_date(sage,'yyyy-mm-dd'))/365
from student;

39、查询本月过生日的学生

select *
from student 
where to_date(sage,'yyyy-mm-dd')>=trunc(sysdate,'mm')
and to_date(sage,'yyyy-mm-dd')<trunc(add_months(sysdate,1),'mm');

40、查询年龄最大的学生

select * from (
select * from student 
order by sage
) t where rownum<=1;