【数据库】MySQL经典面试题（练习）
一、删除除了学号字段以外，其它字段都相同的冗余记录，只保留一条！（也就是要删除凤姐和田七中一条重复数据只留一条）
要求结果数据：
原始数据：
CREATE TABLE tbl_students (
id number(32) NOT NULL,
name varchar(10) DEFAULT NULL,
sax varchar(10) DEFAULT NULL,
age number(6) DEFAULT NULL,
PRIMARY KEY (id)
)
insert into tbl_students (id, name, sax, age) values('2','李四','男','21');
insert into tbl_students (id, name, sax, age) values('3','张三','女','17');
insert into tbl_students (id, name, sax, age) values('4','李四','男','12');
insert into tbl_students (id, name, sax, age) values('6','凤姐','女','20');
insert into tbl_students (id, name, sax, age) values('5','凤姐','女','20');
insert into tbl_students (id, name, sax, age) values('7','田七','男','18');
insert into tbl_students (id, name, sax, age) values('1','田七','男','18');
insert into tbl_students (id, name, sax, age) values('8','张三','男','17');
答案：
mySql
DELETE FROM student WHERE sid NOT IN (SELECT sid FROM ((SELECT MIN(sid) sid FROM student GROUP BY sName,sSex ))t)
oracle：
DELETE FROM student WHERE sid NOT IN(SELECT MIN(sid) sid FROM student GROUP BY sName,sSex )
二、查询各科成绩都及格的学员
（要求查询出参加考试的各科成绩都高于60分，不管参加了多少科考试）
要求结果：
表：
CREATE TABLE tbl_score (
id NUMBER(10) NOT NULL,
username varchar(20) DEFAULT NULL,
course varchar(20) DEFAULT NULL,
score NUMBER(10) DEFAULT NULL,
PRIMARY KEY (id)
)
数据：
insert into tbl_score (id, username, course, score) values('1','张三','语文','50');
insert into tbl_score (id, username, course, score) values('2','张三','数学','80');
insert into tbl_score (id, username, course, score) values('3','张三','英语','90');
insert into tbl_score (id, username, course, score) values('4','李四','语文','70');
insert into tbl_score (id, username, course, score) values('5','李四','数学','80');
insert into tbl_score (id, username, course, score) values('6','李四','英语','80');
insert into tbl_score (id, username, course, score) values('7','王五','语文','50');
insert into tbl_score (id, username, course, score) values('8','王五','英语','70');
insert into tbl_score (id, username, course, score) values('9','赵六','数学','90');
答案：
select username,scor from tbl where id not in (select id from tbl where score < 60)
MySQL题型练习
表（MYSQL）
Student(sid,Sname,Sage,Ssex) 学生表
CREATE TABLE student (
sid varchar(10) NOT NULL,
sName varchar(20) DEFAULT NULL,
sAge datetime DEFAULT '1980-10-12 23:12:36',
sSex varchar(10) DEFAULT NULL,
PRIMARY KEY (sid)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
Course(cid,Cname,tid) 课程表
CREATE TABLE course (
cid varchar(10) NOT NULL,
cName varchar(10) DEFAULT NULL,
tid int(20) DEFAULT NULL,
PRIMARY KEY (cid)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
SC(sid,cid,score) 成绩表
CREATE TABLE sc (
sid varchar(10) DEFAULT NULL,
cid varchar(10) DEFAULT NULL,
score int(10) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
Teacher(tid,Tname) 教师表
CREATE TABLE taacher (
tid int(10) DEFAULT NULL,
tName varchar(10) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
数据：（MySQL）
insert into taacher(tid,tName) values (1,'李老师'),(2,'何以琛'),(3,'叶平');
insert into student(sid,sName,sAge,sSex) values ('1001','张三丰','1980-10-12 23:12:36','男'),('1002','张无极','1995-10-12 23:12:36','男'),('1003','李奎','1992-10-12 23:12:36','女'),('1004','李元宝','1980-10-12 23:12:36','女'),('1005','李世明','1981-10-12 23:12:36','男'),('1006','赵六','1986-10-12 23:12:36','男'),('1007','田七','1981-10-12 23:12:36','女');
insert into sc(sid,cid,score) values ('1','001',80),('1','002',60),('1','003',75),('2','001',85),('2','002',70),('3','004',100),('3','001',90),('3','002',55),('4','002',65),('4','003',60);
insert into course(cid,cName,tid) values ('001','企业管理',3),('002','马克思',3),('003','UML',2),('004','数据库',1),('005','英语',1);
（扩展Oracle）
ORACLE(表+数据)
CREATE TABLE student (
sid varchar2(10) NOT NULL,
sName varchar2(20) DEFAULT NULL,
sAge date ,
sSex varchar2(10) DEFAULT NULL,
PRIMARY KEY (sid)
)
CREATE TABLE course (
cid varchar2(10) NOT NULL,
cName varchar2(10) DEFAULT NULL,
tid number(20) DEFAULT NULL,
PRIMARY KEY (cid)
)
CREATE TABLE sc (
sid varchar2(10) DEFAULT NULL,
cid varchar2(10) DEFAULT NULL,
score number(10) DEFAULT NULL
)
CREATE TABLE teacher (
tid number(10) DEFAULT NULL,
tName varchar2(10) DEFAULT NULL
)
insert into course(cid,cName,tid) values ('001','企业管理',3);
insert into course(cid,cName,tid) values ('002','马克思',3);
insert into course(cid,cName,tid) values ('004','数据库',1);
insert into course(cid,cName,tid) values ('005','英语',1);
insert into sc(sid,cid,score) values ('1001','001',80);
insert into sc(sid,cid,score) values ('1001','002',60);
insert into sc(sid,cid,score) values ('1001','003',70);
insert into sc(sid,cid,score) values ('1002','001',85);
insert into sc(sid,cid,score) values ('1002','002',70);
insert into sc(sid,cid,score) values ('1003','004',90);
insert into sc(sid,cid,score) values ('1003','001',90);
insert into sc(sid,cid,score) values ('1003','002',99);
insert into sc(sid,cid,score) values ('1004','002',65);
insert into sc(sid,cid,score) values ('1004','003',50);
insert into sc(sid,cid,score) values ('1005','005',80);
insert into sc(sid,cid,score) values ('1005','004',70);
insert into sc(sid,cid,score) values ('1003','003',10);
insert into sc(sid,cid,score) values ('1003','005',10);
insert into student(sid,sName,sAge,sSex) values ('1001','张三丰',to_date('1980-10-12 23:12:36','YYYY-MM-DD HH24:MI:SS'),'男');
insert into student(sid,sName,sAge,sSex) values ('1002','张无极',to_date('1995-10-12 23:12:36','YYYY-MM-DD HH24:MI:SS'),'男');
insert into student(sid,sName,sAge,sSex) values ('1003','李奎',to_date('1992-10-12 23:12:36','YYYY-MM-DD HH24:MI:SS'),'女');
insert into student(sid,sName,sAge,sSex) values ('1004','李元宝',to_date('1980-10-12 23:12:36','YYYY-MM-DD HH24:MI:SS'),'女');
insert into student(sid,sName,sAge,sSex) values ('1005','李世明',to_date('1981-10-12 23:12:36','YYYY-MM-DD HH24:MI:SS'),'男');
insert into student(sid,sName,sAge,sSex) values ('1006','赵六',to_date('1986-10-12 23:12:36','YYYY-MM-DD HH24:MI:SS'),'男');
insert into student(sid,sName,sAge,sSex) values ('1007','田七',to_date('1981-10-12 23:12:36','YYYY-MM-DD HH24:MI:SS'),'女');
insert into teacher(tid,tName) values (1,'李老师');
insert into teacher(tid,tName) values (2,'何以琛');
insert into teacher(tid,tName) values (3,'叶平');
SQL问题：
1.查询“001”课程比“002”课程成绩高的所有学生的学号;
select a.sid from (select sid,score from SC where cid='001') a,(select sid,score
from SC where cid='002') b
where a.score>b.score and a.sid=b.sid;
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,Student.Sname,count(SC.cid),sum(score)
from Student left Outer 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(Tname))
from Teacher
where Tname like '李%';
5、查询没学过“叶平”老师课的同学的学号、姓名;
select Student.sid,Student.Sname
from Student
where sid not in (select distinct( SC.sid) from SC,Course,Teacher where SC.cid=Course.cid and Teacher.tid=Course.tid and Teacher.Tname='叶平');
6、查询学过“001”并且也学过编号“002”课程的同学的学号、姓名;
A:select Student.sid,Student.Sname from Student,SC where Student.sid=SC.sid and SC.cid='001'and exists( Select * from SC as SC_2 where SC_2.sid=SC.sid and SC_2.cid='002');
B:SELECT s.sid,s.sName
FROM student s, (SELECT sid,COUNT(cid) FROM sc WHERE cid IN ('001','002') GROUP BY sid HAVING COUNT(cid)>=2) t WHERE s.sid = t.sid
7、查询学过“叶平”老师所教的所有课的同学的学号、姓名;
select sid,Sname
from Student
where sid in (select sid from SC ,Course ,Teacher where SC.cid=Course.cid and Teacher.tid=Course.tid and Teacher.Tname='叶平' group by sid having count(SC.cid)=(select count(cid) from Course,Teacher where Teacher.tid=Course.tid and Tname='叶平'));
8、查询课程编号“002”的成绩比课程编号“001”课程低的所有同学的学号、姓名;
1>Select sid,Sname from (select Student.sid,Student.Sname,score ,(select score from SC SC_2 where SC_2.sid=Student.sid and SC_2.cid='002') score2
from Student,SC where Student.sid=SC.sid and cid='001') S_2 where score2 <score;
2>SELECT s.sid,s.sName FROM student s,
(SELECT sid,score FROM sc WHERE cid = '001') sc_1,
(SELECT sid,score FROM sc WHERE cid = '002') sc_2
WHERE sc_1.sid = sc_2.sid AND s.sid = sc_2.sid AND sc_2.score < sc_1.score
9、查询所有课程成绩小于60分的同学的学号、姓名;
select sid,Sname
from Student
where sid not in (select Student.sid from Student,SC where S.sid=SC.sid and score>60);
10、查询没有学全所有课的同学的学号、姓名;
1>select Student.sid,Student.Sname
from Student,SC
where Student.sid=SC.sid group by Student.sid,Student.Sname having count(cid) <(select count(cid) from Course);
2>SELECT s.sid,s.sname FROM student s,
(SELECT sid,COUNT(cid) FROM sc GROUP BY sid HAVING COUNT(cid) < (SELECT COUNT(cid) FROM course) )t
WHERE s.sid = t.sid
11、查询至少有一门课与学号为“1001”的同学所学相同的同学的学号和姓名;
select sid,Sname from Student,SC where Student.sid=SC.sid and cid in (select cid from SC where sid='1001');
13、把“SC”表中“叶平”老师教的课的成绩都更改为此课程的平均成绩;
UPDATE sc,(SELECT c.cid,AVG(score) avgs FROM sc,course c,teacher t WHERE sc.cid = c.cid AND
c.tid = t.tid AND t.tName = '叶平' GROUP BY c.cid)sc_2 SET sc.score = sc_2.avgs WHERE sc.cid = sc_2.cid
14、查询和“1002”号的同学学习的课程完全相同的其他同学学号和姓名;
select sid from SC where cid in (select cid from SC where sid='1002')
group by sid having count(*)=(select count(*) from SC where sid='1002');
15、删除学习“叶平”老师课的SC表记录;
DELETE FROM sc WHERE sc.cid IN (SELECT sc.cid FROM course c ,teacher t WHERE sc.cid = c.cid AND c.tid = t.tid AND t.tName = '叶平')
17、按平均成绩从高到低显示所有学生的“数据库”、“企业管理”、“英语”三门的课程成绩，按如下形式显示： 学生ID,,数据库,企业管理,英语,有效课程数,有效平均分
SELECT sid as 学生ID
,(SELECT score FROM SC WHERE SC.sid=t.sid AND cid='004') AS 数据库
,(SELECT score FROM SC WHERE SC.sid=t.sid AND cid='001') AS 企业管理
,(SELECT score FROM SC WHERE SC.sid=t.sid AND cid='005') AS 英语
,COUNT(*) AS 有效课程数, AVG(t.score) AS 平均成绩
FROM SC AS t
GROUP BY sid
ORDER BY avg(t.score)
18、查询各科成绩最高和最低的分：以如下形式显示：课程ID，最高分，最低分
select cid "课程ID",max(score) "最高分",min(score) "最低分" from sc group by cid
19、按各科平均成绩从低到高和及格率的百分数从高到低排序
oracle>
SELECT t.cid AS 课程号,MAX(course.Cname)AS 课程名,nvl(AVG(score),0) AS 平均成绩,100 * SUM(CASE WHEN nvl(score,0)>=60 THEN 1 ELSE 0 END)/COUNT(*) AS 及格百分数
FROM SC T,Course
WHERE t.cid=course.cid
GROUP BY t.cid
ORDER BY 100 * SUM(CASE WHEN nvl(score,0)>=60 THEN 1 ELSE 0 END)/COUNT(*) DESC
Mysql>
SELECT t.cid AS 课程号,MAX(course.Cname)AS 课程名,IFNULL(AVG(score),0) AS 平均成绩,100 * SUM(CASE WHEN IFNULL(score,0)>=60 THEN 1 ELSE 0 END)/COUNT(*) AS 及格百分数
FROM SC T,Course
WHERE t.cid=course.cid
GROUP BY t.cid
ORDER BY 100 * SUM(CASE WHEN IFNULL(score,0)>=60 THEN 1 ELSE 0 END)/COUNT(*) DESC
20、查询如下课程平均成绩和及格率的百分数(用"1行"显示): 企业管理（001），马克思（002），OO&UML （003），数据库（004）
SELECT SUM(CASE WHEN cid ='001' THEN score ELSE 0 END)/SUM(CASE cid WHEN '001' THEN 1 ELSE 0 END) AS 企业管理平均分
,100 * SUM(CASE WHEN cid = '001' AND score >= 60 THEN 1 ELSE 0 END)/SUM(CASE WHEN cid = '001' THEN 1 ELSE 0 END) AS 企业管理及格百分数
,SUM(CASE WHEN cid = '002' THEN score ELSE 0 END)/SUM(CASE cid WHEN '002' THEN 1 ELSE 0 END) AS 马克思平均分
,100 * SUM(CASE WHEN cid = '002' AND score >= 60 THEN 1 ELSE 0 END)/SUM(CASE WHEN cid = '002' THEN 1 ELSE 0 END) AS 马克思及格百分数
,SUM(CASE WHEN cid = '003' THEN score ELSE 0 END)/SUM(CASE cid WHEN '003' THEN 1 ELSE 0 END) AS UML平均分
,100 * SUM(CASE WHEN cid = '003' AND score >= 60 THEN 1 ELSE 0 END)/SUM(CASE WHEN cid = '003' THEN 1 ELSE 0 END) AS UML及格百分数
,SUM(CASE WHEN cid = '004' THEN score ELSE 0 END)/SUM(CASE cid WHEN '004' THEN 1 ELSE 0 END) AS 数据库平均分
,100 * SUM(CASE WHEN cid = '004' AND score >= 60 THEN 1 ELSE 0 END)/SUM(CASE WHEN cid = '004' THEN 1 ELSE 0 END) AS 数据库及格百分数
FROM SC
21、查询不同老师所教不同课程平均分从高到低显示 要求显示：教师ID,教师姓名，课程ID,课程名称，平均成绩
SELECT MAX(t.tid) "教师ID",MAX(t.tName) "教师姓名",c.cid "课程ID", MAX(c.cName) "课程名称" ,AVG(sc.score) "平均成绩"
FROM sc,course c,teacher t WHERE sc.cid = c.cid AND c.tid = t.tid GROUP BY c.tid,c.cid
ORDER BY AVG(sc.score) DESC
23、统计列印各科成绩,各分数段人数:课程ID,课程名称,[100-85],[85-70],[70-60],[ <60]
SELECT SC.cid as 课程ID, Cname as 课程名称
,SUM(CASE WHEN score BETWEEN 85 AND 100 THEN 1 ELSE 0 END) AS [100 - 85]
,SUM(CASE WHEN score BETWEEN 70 AND 85 THEN 1 ELSE 0 END) AS [85 - 70]
,SUM(CASE WHEN score BETWEEN 60 AND 70 THEN 1 ELSE 0 END) AS [70 - 60]
,SUM(CASE WHEN score < 60 THEN 1 ELSE 0 END) AS [60 -]
FROM SC,Course
where SC.cid=Course.cid
GROUP BY SC.cid,Cname;
26、查询每门课程被选修的学生数
select cid,count(sid) from sc group by cid;
27、查询出只选修了一门课程的全部学生的学号和姓名
select SC.sid,Student.Sname,count(cid) AS 选课数
from SC ,Student
where SC.sid=Student.sid group by SC.sid ,Student.Sname having count(cid)=1;
28、查询男生、女生人数
Select count(Ssex) as 男生人数 from Student group by Ssex having Ssex='男';
Select count(Ssex) as 女生人数 from Student group by Ssex having Ssex='女';
29、查询姓“张”的学生名单
SELECT Sname FROM Student WHERE Sname like '张%';
30、查询同名同性学生名单，并统计同名人数
SELECT sName,sSex ,COUNT(*) FROM student GROUP BY sName,sSex HAVING COUNT(*) > 1
31、1981年出生的学生名单(注：Student表中Sage列的类型是datetime)
Mysql>
select Sname, CONVERT(char (11),DATEPART(year,Sage)) as age
from student
where CONVERT(char(11),DATEPART(year,Sage))='1981';
Oracle>
select * from student where substr(to_char(sage,'yyyy-MM-dd'),1,4)= '1981'
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) from SC group by cid order by Avg(score),cid DESC ;
33、查询平均成绩大于85的所有学生的学号、姓名和平均成绩
select Sname,SC.sid ,avg(score)
from Student,SC
where Student.sid=SC.sid group by SC.sid,Sname having avg(score)>85;
34、查询课程名称为“数据库”，且分数低于60的学生姓名和分数
Select Sname,isnull(score,0)
from Student,SC,Course
where SC.sid=Student.sid and SC.cid=Course.cid and Course.Cname='数据库'and score <60;
35、查询所有学生的选课情况;
SELECT SC.sid,SC.cid,Sname,Cname
FROM SC,Student,Course
where SC.sid=Student.sid and SC.cid=Course.cid ;
36、查询任何一门课程成绩在70分以上的姓名、课程名称和分数;
SELECT distinct student.sid,student.Sname,SC.cid,SC.score
FROM student,Sc
WHERE SC.score>=70 AND SC.sid=student.sid;
37、查询不及格的课程，并按课程号从大到小排列
select cid from sc where scor e <60 order by cid ;
38、查询课程编号为003且课程成绩在80分以上的学生的学号和姓名;
select SC.sid,Student.Sname from SC,Student where SC.sid=Student.sid and Score>80 and cid='003';
39、求选了课程的学生人数
select count(*) from sc;
40、查询选修“叶平”老师所授课程的学生中，成绩最高的学生姓名及其成绩
select Student.Sname,score
from Student,SC,Course C,Teacher
where Student.sid=SC.sid and SC.cid=C.cid and C.tid=Teacher.tid and Teacher.Tname='叶平' and SC.score=(select max(score)from SC where cid=C.cid );
41、查询各个课程及相应的选修人数
select count(*) from sc group by cid;
42、查询不同课程成绩相同的学生的学号、课程号、学生成绩
select distinct A.sid,B.score from SC A ,SC B where A.Score=B.Score and A.cid <>B.cid ;
43、查询每门功课成绩最好的前两名
SELECT *
FROM sc t1
WHERE (
SELECT COUNT(*)
FROM sc t2
WHERE t1.cid=t2.cid
AND t2.score>=t1.score
) <=2 ORDER BY t1.cid
44、统计每门课程的学生选修人数（超过10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 "课程号",COUNT(*) "选修人数" FROM sc GROUP BY cid HAVING COUNT(*) >10 ORDER BY COUNT(*) DESC,cid
45、检索至少选修两门课程的学生学号
select sid
from sc
group by sid
having count(*) > = 2
46、查询全部学生都选修的课程的课程号和课程名
SELECT s.sName,c.cName, COUNT(*) FROM student s,course c, sc WHERE s.sid = sc.sid AND sc.cid = c.cid GROUP BY sc.cid HAVING COUNT(*) = (SELECT COUNT(*) FROM student)
47、查询没学过“叶平”老师讲授的任一门课程的学生姓名
SELECT DISTINCT Sname FROM Student WHERE sid NOT IN (SELECT sid FROM Course,Teacher,SC WHERE Course.tid=Teacher.tid AND SC.cid=course.cid AND Tname='叶平');
48、查询两门以上不及格课程的同学的学号及其平均成绩
select sid,avg(ifnull(score,0)) from SC where sid in (select sid from SC where score <60 group by sid having count(*)>2)group by sid;
49、检索“004”课程分数小于60，按分数降序排列的同学学号
select sid from SC where cid='004'and score <60 order by score desc;
50、删除“1002”同学的“001”课程的成绩
delete from Sc where sid='1002' and cid='001';
行转列
CREATE TABLE stu_score (
grade_id varchar(10) DEFAULT NULL,
subject_name varchar(10) DEFAULT NULL,
max_score int(10) DEFAULT NULL
)
insert into `stu_score`(`grade_id`,`subject_name`,`max_score`) values('1','语文',98);
insert into `stu_score`(`grade_id`,`subject_name`,`max_score`) values('2','数学',95);
insert into `stu_score`(`grade_id`,`subject_name`,`max_score`) values('2','政治',87);
insert into `stu_score`(`grade_id`,`subject_name`,`max_score`) values('5','语文',97);
insert into `stu_score`(`grade_id`,`subject_name`,`max_score`) values('5','数学',100);
insert into `stu_score`(`grade_id`,`subject_name`,`max_score`) values('5','政治',92);
1.查询出要求的结果格式
SELECT
CASE grade_id WHEN 1 THEN '一年级'
WHEN 2 THEN '二年级'
WHEN 5 THEN '五年级'
END AS '年级',
CASE subject_name WHEN '语文' THEN max_score END AS '语文',
CASE subject_name WHEN '数学' THEN max_score END AS '数学',
CASE subject_name WHEN '政治' THEN max_score END AS '政治'
FROM stu_score
2,去除null
SELECT
CASE grade_id WHEN 1 THEN '一年级'
WHEN 2 THEN '二年级'
WHEN 5 THEN '五年级'
END AS '年级',
IFNULL(CASE subject_name WHEN '语文' THEN max_score END,0) AS '语文',
IFNULL(CASE subject_name WHEN '数学' THEN max_score END,0) AS '数学',
IFNULL(CASE subject_name WHEN '政治' THEN max_score END,0) AS '政治'
FROM stu_score
3.合并结果。
SELECT
CASE grade_id WHEN 1 THEN '一年级'
WHEN 2 THEN '二年级'
WHEN 5 THEN '五年级'
END AS '年级',
MAX(IFNULL(CASE subject_name WHEN '语文' THEN max_score END,0)) AS '语文',
MAX(IFNULL(CASE subject_name WHEN '数学' THEN max_score END,0)) AS '数学',
MAX(IFNULL(CASE subject_name WHEN '政治' THEN max_score END,0)) AS '政治'
FROM stu_score
GROUP BY grade_id
