mysql数据库查询练习

Posted 2020-12-08 QMH

创建四张数据表

学生表student：学号，姓名，性别，出生年月日，所在班级

教师表teacher：教师编号，教师名，教师性别，出生年月日，职称，所在部门

课程表course：课程号，课程名，教师编号

成绩表score：学号，课程号，成绩

添加信息：

学生表：

insert into student values (\'1001\',\'老大\',\'男\',\'1999-08-01\',\'2000\');
insert into student values (\'1002\',\'老二\',\'女\',\'1999-08-02\',\'2000\');
insert into student values (\'1003\',\'老三\',\'男\',\'1999-08-03\',\'2001\');
insert into student values (\'1004\',\'老四\',\'女\',\'1999-08-04\',\'2001\');
insert into student values (\'1005\',\'老五\',\'男\',\'1999-08-05\',\'2002\');
insert into student values (\'1006\',\'老六\',\'男\',\'1999-08-06\',\'2002\');
insert into student values (\'1007\',\'老七\',\'男\',\'1999-08-07\',\'2003\');
insert into student values (\'1008\',\'老八\',\'女\',\'1999-08-08\',\'2004\');

教师表：

insert into teacher values(\'201\',\'王菊\',\'女\',\'1890-10-11\',\'副教授\',\'计算机系\');
insert into teacher values(\'202\',\'李平\',\'男\',\'1890-10-11\',\'教授\',\'电子工程系\');
insert into teacher values(\'203\',\'张利\',\'男\',\'1890-10-11\',\'副教授\',\'自动化系\');
insert into teacher values(\'204\',\'王霞\',\'女\',\'1890-10-11\',\'讲师\',\'电子工程系\');
insert into teacher values(\'205\',\'刘杰\',\'男\',\'1890-10-11\',\'助教\',\'计算机系\');

课程表：

insert into course values (\'3-101\',\'计算机基础\',\'201\');
insert into course values (\'3-102\',\'高等数学\',\'202\');
insert into course values (\'3-103\',\'操作系统\',\'203\');
insert into course values (\'3-104\',\'概率论\',\'204\');
insert into course values (\'3-105\',\'概率论\',\'205\');

成绩表：

insert into score values (\'1001\',\'3-101\',\'98\');
insert into score values (\'1001\',\'3-103\',\'97\');
insert into score values (\'1002\',\'3-101\',\'88\');
insert into score values (\'1003\',\'3-104\',\'78\');
insert into score values (\'1004\',\'3-103\',\'98\');
insert into score values (\'1006\',\'3-101\',\'77\');
insert into score values (\'1008\',\'3-104\',\'55\');
insert into score values (\'1001\',\'3-102\',\'98\');
insert into score values (\'1007\',\'3-105\',\'67\')

查询练习：

1.查询student表的所有记录；

select * from student

　

2.查询student表的sname，ssex,class列；

select sname,ssex,class from student 

　

3.查询教师所有的部门，不重复显示

select distinct depart  from teacher 

　

4.查询成绩表中成绩在77-88之间的所有记录

select *  from score  where degree between \'77\' and \'88\'

由查询的数据可知，between...and查询的结果包括两端的值 

select *  from score  where degree>77 and degree<88

　

 由查询数据可知，直接使用运算符比较不包含两端数据 

5.查询成绩为98，88，或77的记录

select *  from score  where degree = \'77\' or degree = \'88\' or degree = \'98\'

select *  from score  where degree  in (77,88,98)　　（in表示或者的关系）

6.查询学生表中1001班或性别为女的学生记录

select *  from student  where class=\'2000\' or ssex = \'女\'

 

7.以class降序查询学生表的所有记录

select *  from student  order by class desc

 

8.以cno升序，degree降序查询成绩表的所有记录

select *  from score  order by cno asc , degree desc 

9.查询2000班的所有学生人数

select count(*) from student where class = 2000

10.查询成绩表中的最高分的学生号和课程号（子查询）

select sno,cno from score where degree=(select max(degree) from score)

 11.查询每门课的平均成绩（分组查询group by）

select cno,avg(degree)from score group by cno 

12.查询score 表中至少有2名学生选修的并以3开头的课程的平均成绩（具有条件的分组查询group by....having，模糊查询）

select cno,count(cno),avg(degree) from score group by cno having count(cno)>=2 and cno like\'3%\'

13.查询分数大于70，小于90的sno列

select sno,degree from score where degree between 70 and 90

select sno,degree from score where degree>70 and degree<90

 14.查询所有学生的sname,cno,degree列（多表查询）

select sname,cno,degree from student,score where student.sno = score.sno

 

 15.查询所有学生的sno,cname,degree的列（多表联查）

select sno,cname,degree from course,score where course.cno = score.cno

 

 16.查询所有学生的sname,cname,degree(三表联查，找到一个中间表，另两个表与中间表产生联系)

select sname,cname,degree from student,course,score where student.sno= score.sno and course.cno = score.cno

 17.查询“2000”班学生每门课的平均成绩

（1）2000班的学生的学号

select * from student where class=\'2000\'

select  sno  from student where class=\'2000\'

(2)根据（1）学生号查询2000班的学生成绩表

select * from score where sno in (select sno from student where class=\'2000\')

select cno,degree from score where sno in (select sno from student where class=\'2000\')

（3）根据（2）中的cno对学科进行分组求平均分

select cno,avg(degree) from score where sno in (select sno from student where class=\'2000\') group by cno

 

 18.查询选修“3-101”课程的成绩高于“1006”号同学选修“3-101”成绩的所有同学的记录

（1）查选“1006”号同学选修3-101课的成绩

select * from score where cno=\'3-101\' and sno=\'1006\'

（2）查询选修“3-101”课程的成绩高于“1006”号同学选修“3-101”成绩的所有同学的记录

select * from score where degree>(select degree from score where cno=\'3-101\' and sno=\'1006\')and cno=\'3-101\'

 19.查询成绩高于学号“1006”、课程号为“3-101”的成绩的所有记录

（1）查选“1006”号同学选修3-101课的成绩

select * from score where cno=\'3-101\' and sno=\'1006\'

（2）查询成绩高于学号“1006”、课程号为“3-101”的成绩的所有记录

select * from score where degree>(select degree from score where cno=\'3-101\' and sno=\'1006\')

 

 20.查询学号为1008、1001的同学的同年出生的所有学生的sno\\sname\\sbrithday列

（1）查询学号为1008、1001的同学的同年出生
select year(sbrithday) from student where sno in (\'1001\',\'1008\')

（2）查询学号为1008、1001的同学的同年出生的所有学生的sno\\sname\\sbrithday列
select sno,sname,sbrithday from student where year(sbrithday) =(select year(sbrithday) from student where sno in (\'1001\',\'1008\'))

 21.查询王菊老师任课的学生成绩

（1）查询王菊老师的课程号

select cno from teacher as t,course as c where t.tno=c.tno

（2）查询王菊老师任课的学生成绩

select sno,degree from score where cno=(select cno from teacher as t,course as c where t.tno=c.tno and tname=\'王菊\')

 22.查询选修某课程的学生人数多于2人的教师姓名

（1）根据课程号查询选修人数大于2人的课程号（group by的条件分组查询）

select cno from score  group by cno having count(cno)>2

（2）根据（1）查询出课程表中的教师号

select tno from course where cno =(select cno from score group by cno having count(cno)>2)

（3）根据教师号查询教师名字

select tname from teacher where tno=(select tno from course where cno =(select cno from score group by cno having count(cno)>2))

 23.查询2000班和2001班的学生记录（或的使用，In，or）

select * from student where class in(\'2000\',\'2001\')

select * from student where class =\'2000\' or class=\'2001\'

　24.查询计算机系老师所教课程的成绩

（1）查询计算机系老师的教师号

select tno from teacher where depart=\'计算机系\'

（2）根据教师号查询老师对应的课程号

select cno from course where tno in (select tno from teacher where depart=\'计算机系\')

（3）根据课程号查询成绩

select cno,degree from score where cno in (select cno from course where tno in (select tno from teacher where depart=\'计算机系\'))

 25.查询计算机系和电子工程系不同职称的教师姓名和职称prof（这两个系中职称相同的舍去）

（1）查询电子工程系的所有老师的职称

select prof from teacher where depart = \'计算机系\'

　　  查询计算机系的所有老师的职称

select prof from teacher where depart = \'电子工程系\'

（2）查询计算机系中与电子工程系中不同的职称

select prof from teacher where depart = \'计算机系\' and prof not in (select prof from teacher where depart = \'电子工程系\')

　　  查询电子工程系中与计算机系中不同的职称

select prof from teacher where depart = \'电子工程系\' and prof not in (select prof from teacher where depart = \'计算机系\')

（3）使用union将（2）中的语句进行联合（求并集），得出两个系中不同的职称

select prof from teacher where depart = \'电子工程系\' and prof not in (select prof from teacher where depart = \'计算机系\')

union

select prof from teacher where depart = \'计算机系\' and prof not in (select prof from teacher where depart = \'电子工程系\')

 

 26.查询选修编号为“3-101”课程且成绩至少高于选修编号为“3-102”的同学的cno,sno,degree,并按成绩由高到底排列

（1）查询出选修“3-102”学生的成绩

select degree from score where cno=\'3-102\'

（2）查询出选修3-101课程的成绩至少大于3-102的学生cno,sno,degree的信息（至少any：只需要满足3-101中的成绩大于3-102中的最低成绩即可）

select cno,sno,degree from score where degree>any(select degree from score where cno=\'3-102\') and cno =\'3-101\'

（3）根据（2）的成绩降序排列（order by  ... desc）

select cno,sno,degree from score where degree>any(select degree from score where cno=\'3-102\') and cno =\'3-101\' order by degree desc

 27.查询选修编号为“3-101”课程且成绩高于选修编号为“3-102”的同学的cno,sno,degree

（1）查询出选修“3-102”学生的成绩

select degree from score where cno=\'3-102\'

（2）查询出选修3-101课程的成绩大于3-102的学生cno,sno,degree的信息（且all:高于3-102班的最高成绩才满足）

select cno,sno,degree from score where degree>all(select degree from score where cno=\'3-102\') and cno =\'3-101\'

 28.查询所有教师和学生的name,sex,brithday(求并集union)

select sname as name,ssex as sex,sbrithday as brithday from student 
union 
select tname as name,tsex as sex,tbrithday as brithday from teacher

29.查询成绩比该成绩平均分低的同学的成绩表

（1）查询每一门课的平均成绩

select  avg(degree) from score b group by cno

（2）通过采用复制表结构的方法做条件查询（保证使用的cno是相同的）

select * from score a where degree<(select avg(degree) from score b where a.cno=b.cno)

30.查询至少有两名男生的班级

select  count(ssex),class from student where ssex=\'男\' group by class having count(ssex)>=2

 31.查询student表中不含“老”字的同学记录

select * from student where sname not like\'老%\'

32.查询student表中每个学生的姓名和年龄

年龄=当前年份-出生年份

（1）当前年份

select year(now())

（2）学生出生年份

select year(sbrithday) from student 

（3）每个学生的姓名和年龄

select sname,year(now())-year(sbrithday) as age from student

 

 33.以班号和年龄从大到小查询student表中所有同学的信息

select * from student  order by class desc,sbrithday

34.按等级查询

创建一个等级表

create  table grade(low int(3),upp int(3),grade char(4))

插入数据

insert into grade values (90,100,\'a\');

insert into grade values (80,89,\'b\');

insert into grade values (70,79,\'c\');

insert into grade values (60,69,\'d\');

insert into grade values (0,59,\'e\');

查询所有学生的sno,cno,grade

select sno,cno,grade from score,grade where score.degree between grade.low and grade.upp

 35.sql的四种连接查询

内连接：inner join 或 join

外连接：

左外连接：left join ...on或 left outer join ...on

右外连接：right join...on 或 right outer join...on

完全外连接：full join...on 或 full outer join...on

创建两张表：

person 表：id,name,cardId

card 表 ：id，name

create table person (id int (10) primary key ,name varchar(20),cardid int(10) );

create table card (id int(10) primary key ,name varchar (20) );

向两张表中分别添加数据

insert into card values(1,\'饭卡\');

insert into card values(2,\'地铁卡\');

insert into card values(3,\'工商卡\');

 insert into card values(4,\'邮政卡\');

insert into card values(5,\'农行卡\');

insert into person values(1,\'老大\',1);

insert into person values(2,\'老二\',4);

insert into person values(3,\'老三\',5);

insert into person values(4,\'老四\',2);

insert into person values(5,\'老五\',2);

insert into person values(6,\'老六\',6);

注意到person表中并没有创建外键

（1）内连接（jion ...on）,查询出两张表有关联的信息（即两表共有的部分）

 select * from person join card on person.cardId=card.id

 select * from person inner join card on person.cardId=card.id

（2）左外连接：会把左边表里的所有数据取出来，而右边表中的数据，如果有相等的就显示出来，若没有就显示为空

select * from person left join card on person.cardId=card.id

（3）右外连接：会把右边表里的所有数据取出来，而左边表中的数据，如果有相等的就显示出来，若没有就显示为空

select * from person right join card on person.cardId=card.id

 

（4）全外连接（full join ）,注:mysql 默认不支持此种写法 Oracle支持(select * from person full join card on person.cardId=card.id) ,可以使用将左连接与右连接结合起来作为全连接

select * from person right join card on person.cardId=card.id
union 

select * from person left join card on person.cardId=card.id