MySQL相关十五道面试题分享

目录

表结构

表数据

题目

---

表结构

-- 1.学生表-t_mysql_student
-- sid 学生编号,sname 学生姓名,sage 学生年龄,ssex 学生性别

-- 2.教师表-t_mysql_teacher
-- tid 教师编号,tname 教师名称

-- 3.课程表-t_mysql_course
-- cid 课程编号,cname 课程名称,tid 教师名称

-- 4.成绩表-t_mysql_score
-- sid 学生编号,cid 课程编号,score 成绩

表数据

-- 学生表
insert into t_mysql_student values('01' , '赵雷' , '1990-01-01' , '男');
insert into t_mysql_student values('02' , '钱电' , '1990-12-21' , '男');
insert into t_mysql_student values('03' , '孙风' , '1990-12-20' , '男');
insert into t_mysql_student values('04' , '李云' , '1990-12-06' , '男');
insert into t_mysql_student values('05' , '周梅' , '1991-12-01' , '女');
insert into t_mysql_student values('06' , '吴兰' , '1992-01-01' , '女');
insert into t_mysql_student values('07' , '郑竹' , '1989-01-01' , '女');
insert into t_mysql_student values('09' , '张三' , '2017-12-20' , '女');
insert into t_mysql_student values('10' , '李四' , '2017-12-25' , '女');
insert into t_mysql_student values('11' , '李四' , '2012-06-06' , '女');
insert into t_mysql_student values('12' , '赵六' , '2013-06-13' , '女');
insert into t_mysql_student values('13' , '孙七' , '2014-06-01' , '女');

-- 教师表
insert into t_mysql_teacher values('01' , '张三');
insert into t_mysql_teacher values('02' , '李四');
insert into t_mysql_teacher values('03' , '王五');

-- 课程表
insert into t_mysql_course values('01' , '语文' , '02');
insert into t_mysql_course values('02' , '数学' , '01');
insert into t_mysql_course values('03' , '英语' , '03');

-- 成绩表
insert into t_mysql_score values('01' , '01' , 80);
insert into t_mysql_score values('01' , '02' , 90);
insert into t_mysql_score values('01' , '03' , 99);
insert into t_mysql_score values('02' , '01' , 70);
insert into t_mysql_score values('02' , '02' , 60);
insert into t_mysql_score values('02' , '03' , 80);
insert into t_mysql_score values('03' , '01' , 80);
insert into t_mysql_score values('03' , '02' , 80);
insert into t_mysql_score values('03' , '03' , 80);
insert into t_mysql_score values('04' , '01' , 50);
insert into t_mysql_score values('04' , '02' , 30);
insert into t_mysql_score values('04' , '03' , 20);
insert into t_mysql_score values('05' , '01' , 76);
insert into t_mysql_score values('05' , '02' , 87);
insert into t_mysql_score values('06' , '01' , 31);
insert into t_mysql_score values('06' , '03' , 34);
insert into t_mysql_score values('07' , '02' , 89);
insert into t_mysql_score values('07' , '03' , 98);

题目

考核点：多表联查、内外连接、子查询

01）查询" 01 "课程比" 02 "课程成绩高的学生的信息及课程分数

SELECT
	s.*,
	( CASE WHEN t1.cid = '01' THEN t1.score END ) 语文,
	( CASE WHEN t2.cid = '02' THEN t2.score END ) 数学 
FROM
	t_mysql_student s,
	( SELECT * FROM t_mysql_score sc WHERE sc.cid = '01' ) t1,
	( SELECT * FROM t_mysql_score sc WHERE sc.cid = '02' ) t2 
WHERE
	s.sid = t1.sid 
	AND s.sid = t2.sid 
	AND t1.score > t2.score

02）查询同时存在" 01 "课程和" 02 "课程的情况

SELECT
	s.*,
	( CASE WHEN t1.cid = '01' THEN t1.score END ) 语文,
	( CASE WHEN t2.cid = '02' THEN t2.score END ) 数学 
FROM
	t_mysql_student s,
	( SELECT * FROM t_mysql_score sc WHERE sc.cid = '01' ) t1,
	( SELECT * FROM t_mysql_score sc WHERE sc.cid = '02' ) t2 
WHERE
	s.sid = t1.sid 
	AND s.sid = t2.sid

03）查询存在" 01 "课程但可能不存在" 02 "课程的情况(不存在时显示为 null )

SELECT
	s.*,
	( CASE WHEN t1.cid = '01' THEN t1.score END ) 语文,
	( CASE WHEN t2.cid = '02' THEN t2.score END ) 数学 
FROM
	t_mysql_student s
	INNER JOIN ( SELECT * FROM t_mysql_score sc WHERE sc.cid = '01' ) t1 ON s.sid = t1.sid
	LEFT JOIN ( SELECT * FROM t_mysql_score sc WHERE sc.cid = '02' ) t2 ON s.sid = t2.sid

04）查询不存在" 01 "课程但存在" 02 "课程的情况

SELECT
	s.* ,
	( CASE WHEN sc.cid = '01' THEN sc.score END ) 语文,
	( CASE WHEN sc.cid = '02' THEN sc.score END ) 数学 
FROM
	t_mysql_score sc ,
	t_mysql_student s
WHERE
s.sid=sc.sid and
	sc.sid NOT IN ( SELECT sid FROM t_mysql_score WHERE cid = '01' ) 
	AND sc.cid = '02'

05）查询平均成绩大于等于 60 分的同学的学生编号和学生姓名和平均成绩

SELECT
	s.sid,
	s.sname,
	round( avg( sc.score ) ) 平均成绩 
FROM
	t_mysql_student s,
	t_mysql_score sc 
WHERE
	s.sid = sc.sid 
GROUP BY
	s.sid,
	s.sname 
HAVING
	平均成绩 >= 60

06）查询在t_mysql_score表存在成绩的学生信息

SELECT
	s.sid,
	s.sname
FROM
	t_mysql_student s,
	t_mysql_score sc 
WHERE
	s.sid = sc.sid 
GROUP BY
	s.sid,
	s.sname 

07）查询所有同学的学生编号、学生姓名、选课总数、所有课程的总成绩(没成绩的显示为 null )

SELECT
	s.sid,
	s.sname,
	count( sc.score ) 选课总数,
	sum( sc.score ) 总成绩 
FROM
	t_mysql_student s,
	t_mysql_score sc 
WHERE
	s.sid = sc.sid 
GROUP BY
	s.sid,
	s.sname

08）查询「李」姓老师的数量
09）查询学过「张三」老师授课的同学的信息
10）查询没有学全所有课程的同学的信息
11）查询没学过"张三"老师讲授的任一门课程的学生姓名
12）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
13）检索" 01 "课程分数小于 60，按分数降序排列的学生信息
14）按平均成绩从高到低显示所有学生的所有课程的成绩以及平均成绩
15）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，中等率，优良率，优秀率及格为>=60，中等为：70-80，优良为：80-90，优秀为：>=90
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