4、mysql查询练习

    1、创建四个表供查询

（1）学生表—Student

学号

姓名

性别

出生年月日

所在班级

【语句】

    > create table student(

    -> sno varchar(20) primary key,

    -> sname varchar(20) not null,

    -> ssex varchar(20) not null,

    -> sbirthday datetime,

    -> class varchar(20));

（2）教师表—Teacher

教师编号

教师姓名

教师性别

出生年月日

职称

所在部门

【语句】

    > create table teacher(

    -> tno varchar(20) primary key,

    -> tname varchar(20) not null,

    -> tsex varchar(10) not null,

    -> tbirthday datetime,

    -> prof varchar(20) not null,

    -> depart varchar(20) not null);

（3）课程表—Course

课程号

课程名称

教师编号

【语句】

>create table course(

    -> cno varchar(20) primary key,

    -> cname varchar(20) not null,

    -> tno varchar(20) not null,

    -> foreign key(tno) references teacher(tno));

（4）成绩表—Score

学号

课程号

成绩

【语句】

>create table score(

    -> sno varchar(20) not null,

    -> cno varchar(20) not null,

    -> degree decimal,

    -> foreign key(sno) references student(sno),

    -> foreign key(cno) references course(cno),

    ->primary key(sno,cno));

2、往表中添加数据

//添加学生信息

insert into student values('101','曾华','男','1977-09-01','95033');

insert into student values('102','匡明','男','1975-10-02','95031');

insert into student values('103','王丽','女','1976-01-23','95033');

insert into student values('104','李军','男','1976-02-20','95033');

insert into student values('105','王芳','女','1975-02-10','95031');

insert into student values('106','陆君','男','1974-06-03','95031');

insert into student values('107','王尼玛','男','1976-02-20','95033');

insert into student values('108','张全蛋','男','1975-02-10','95031');

insert into student values('109','赵铁柱','男','1974-06-03','95031');

//添加教师表

insert into teacher values(804,'李成','男','1958-12-02','副教授','计算机系');

insert into teacher values(856,'张旭','男','1969-03-12','讲师','电子工程系');

insert into teacher values(825,'王萍','女','1972-05-05','助教','计算机系');

insert into teacher values(831,'刘冰','女','1977-08-14',' 教','电子 工程系');

//添加课程表

insert into course values('3-105','计算机导论','825');

insert into course values('3-245','操作系统','804');

insert into course values('6-166','数字电路','856');

insert into course values('9-888','高等数学','831');

//添加成绩表

insert into score values('103','3-105','92');

insert into score values('103','3-245','86');

insert into score values('103','6-166','85');

insert into score values('105','3-105','88');

insert into score values('105','3-245','75');

insert into score values('105','6-166','79');

insert into score values('109','3-105','76');

insert into score values('109','3-245','68');

insert into score values('109','6-166','81');

3、查询练习

（1）查询student 表中所有的记录

       > select * from student;

（2）查询部分记录（student表中的sno、sname、ssex）

        > select sno,sname,ssex from student;

（3）查询教师depart中不重复的记录    distinct

        >select distinct depart from teacher;

（4）查询区间（查询score中成绩在60到90的记录）

    ——用between……and……

        >select * from score where degree between 60 and 90;

    ——直接用运算符进行比较

        > select * from score where degree > 60 and degree < 90;

（5）表示或者关系（查询同一字段中指定记录：查询score表中成绩为85，86，88的记录）

        >select * from score where degree in(85,86,88);

（6）表示或者关系（查询不同字段中指定记录：查询student表中“95031”班或者性别为“女” 的记录）

        >select * from student where class='95031' or ssex='女';

（7）升序、降序

    ——以class降序查询student表中所有记录

            >select * from student order by class desc;

    ——以class升序查询student表中所有记录

            > select * from student order by class;（默认为升序）

            > select * from student order by class asc;（或加asc）

（8）以cno升序、degree降序查询score表

        >select * from score order by cno asc,degree desc;（先以cno升序，相同的再以degree降序）

（9）查询“95031”班的学生人数

        >select count(*) from student where class='95031';

（10）查询score表中最高分的学生的学生号和课程号（子查询）

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

【注】1、找到最高分

                >select max(degree) from score

           2、找到最高分学生的学生号和课程号

                >select sno,cno from score where degree=();

——通过排序取出记录

    1、将成绩降序

        >select sno,cno,degree from score order by degree desc;

    2、取记录（用limit，这里取出了一条，当然可以改变取值范围）

        >  select sno,cno,degree from score order by degree desc limit 0,1;

（11）查询每门课的平均成绩

—1—分步查询

    >select cno,avg(degree) from score where cno='3-105';

    > select cno,avg(degree) from score where cno ='3-245';

    >select cno,avg(degree) from score where cno ='6-166';

    >select cno,avg(degree) from score where cno ='9-888';

—2—分组实现  group by

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

（12）查询score表中至少有两名学生选修的并以3开头的课程的平均分数

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

—分析—：

    > select cno from score group by cno;    //分组

    >having count(cno)>=2          //选修>=2

    > cno like'3%'        //以3开头

    >avg(degree)    //求平均值

    >count(*)    //因为现在已经进行了分组，直接记录每个字段所有的人数

（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;

或者

    > 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;

【注】这里因为两个表共同有sno的字段，所以可以对应起来将sname替换过来

（15）查询所有学生的sno、cname、degree

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

（16）查询所有学生的sname、cname、degree（3表查询）

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

【拓展】as可以进行重命名

    >select sname,cname,degree,student.sno as stu_sno,score.sno,course.cno as cou_cno,score.cno from score,course,student where student.sno=score.sno and score.cno=course.cno;

 

通过上述多表查询的练习我们知道，就是通过表与表之间外键联系起来，实现不同表之间的拼接展示

（17）查询“95031” 班学生每门课的平均分

—分析—

查询95031班    

> select * from student where class='95031';

利用子查询通过sto将score中95031班的学生筛选出来

>select * from score where sno in(select sno from student where class='95031');

将课程分组，求出每门课平均分，并查询

select cno,avg(degree) from score where sno in(select sno from student where class='95031') group by cno;

（18）查询选修“3-105”课程同学的成绩高于“109”号同学“3-105”成绩的其他所有同学的记录

    >select * from score where cno = '3-105' and degree > (select degree from score where cno='3-105'and sno='109');

—分析—

  先找到选修3-105并且学号为109的同学的成绩

    >select degree from score where cno='3-105'and sno='109'

  再筛选选修3-105的所有同学

    >select * from score where cno = '3-105' 

二者结合在一起

     >select * from score where cno = '3-105' and degree > (select degree from score where cno='3-105'and sno='109');

（19）查询成绩高于学号为“109”、课程号为“3-105”的同学的成绩的其他同学的记录情况

    > select * from score where degree > (select degree from score where cno='3-105'and sno='109');

只需要满足（18）中的一个条件即可

（20）查询和学号为108、109的同学同年出生的所有学生的sno、sname和sbirthday字段

    > select sno,sname,sbirthday from student where year(sbirthday) in(select year(sbirthday) from student where sno in(108,109));

—分析—

先将学号为108、109的同学的出生年份查询出来

    >select year(sbirthday) from student where sno in(108,109);

再通过子查询查到与上述两位同学同年出生的学生的记录

    > select sno,sname,sbirthday from student where year(sbirthday) in(select year(sbirthday) from student where sno in(108,109));

（21）查询张旭教师任课的学生的成绩（嵌套子查询）

    >>select sname,degree from score,student where score.sno = student.sno and cno = (select cno from course where tno = (select tno from teacher where tname='张旭'));

—分析—

在teacher中先将张旭的tno找到

    >select tno from teacher where tname='张旭'

通过tno在表course中找到所对应的cno

    > select cno from course where tno = (select tno from teacher where tname='张旭');

通过表sname与表student中的sno，将成绩与学生姓名对应起来在满足cno等于上述取出的cno情况下查询出来

    >select sname,degree from score,student where score.sno = student.sno and cno = (select cno from course where tno = (select tno from teacher where tname='张旭'));

（22）查询选修某课程的同学人数多于5人的教师的姓名

【注】从score表中我们已知满足上述问题的没有，现在对score添加几条数据（注意前面的操作用的都是之前的score表）

——新添加的数据——

insert into score values('101','3-105','90');

insert into score values('102','3-105','91');

insert into score values('104','3-105','89');

——之前的数据如下——

insert into score values('103','3-105','92');

insert into score values('103','3-245','86');

insert into score values('103','6-166','85');

insert into score values('105','3-105','88');

insert into score values('105','3-245','75');

insert into score values('105','6-166','79');

insert into score values('109','3-105','76');

insert into score values('109','3-245','68');

insert into score values('109','6-166','81');

继续……

语句： select tname from teacher where tno =( select tno from course where cno =(select cno from score group by cno having count(cno) >5))

—分析—

在表score中查询选修某课程的同学人数多于5人的课程号cno

    >select cno from score group by cno having count(cno) >5;

在表course中查询满足上述cno的教师的tno

    > select tno from course where cno =(select cno from score group by cno having count(cno) >5);

最后在teacher表中查询满足上述tno的老师的tname

    > select tname from teacher where tno =( select tno from course where cno =(select cno from score group by cno having count(cno) >5))

（23）查询95033班和95031班全体学生的记录

【注】我们在这里又新加了一条数据

    > insert into student values('110','张飞','男','1974-06-03','95038');

语句： select * from student where class in('95033','95031');

（24）查询存在有85分以上成绩的课程cno

    >select cno,degree from score where degree >85;

（25）查出“计算机系”教师所教课程的成绩表

    > select * from score where cno in (select cno from course where tno in(select tno from teacher where depart ="计算机系"));

—分析—

先从teacher表中查询计算机系老师的tno

        >select tno from teacher where depart ="计算机系";

从表course中查询到tno满足上述要求的con

        >select cno from course where tno in(select tno from teacher where depart ="计算机系")

从score表中查询满徐上述con的记录

    > select * from score where cno in (select cno from course where tno in(select tno from teacher where depart ="计算机系"));

（26）查询“计算机系”与“电子工程系”不同职称的教师的tname和prof

       理解它的意思是，查询计算机系中电子工程系没有的职称+查询电子工程系中计算机系没有的职称

       查询计算机系中的职称

            >select prof from teacher where depart ="计算机系"

        查询电子工程系中的职称在计算机系没有的记录

             >select tname,prof from teacher where depart ="电子工程系" and prof not in(select prof from teacher where depart ="计算机系");

        同理查询计算机系中的职称在电子工程系中没有的记录

            > 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");

        两者相加    union

            >select tname,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 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");

（27）查询（选修编号为“3-105”且成绩至少高于选修编号为“3-245”的同学任意一位同学的成绩）的cno、sno、degree、将degree按从高到低的次序排列

    >select degree from score where cno ='3-105'and degree > any( select degree from score where cno ='3-245') order by degree desc;

—分析—

选修3-105同学的成绩

    >select degree from score where cno ='3-105'

选修3-245同学的成绩

    >select degree from score where cno ='3-245'

至少高与（高于选修3-245任何一位同学的成绩  >any ）

    >select degree from score where cno ='3-105'and degree > any( select degree from score where cno ='3-245') 

从高到底的次序排列    order by 

    >select degree from score where cno ='3-105'and degree > any( select degree from score where cno ='3-245') order by degree desc;

（28）查询选修编号为“3-105”且成绩高于选修编号为“3-245”课程的同学的cno、sno、degree

    > select degree from score where cno ='3-105'and degree > all( select degree from score where cno ='3-245') order by degree desc;

—分析—

选修3-105同学的成绩

>select degree from score where cno ='3-105'

选修3-245同学的成绩

    >select degree from score where cno ='3-245'

高于（是高于选修3-245的所有同学的成绩）>all

    > select degree from score where cno ='3-105'and degree > all( select degree from score where cno ='3-245') order by degree desc;

（29）查询所有教师和同学的name、sex、和birthday

    >select tname as name,tsex as sex,tbirthday as birthday from teacher union select sname,ssex,sbirthday from student;

—分析—

求教师

    >select tname,tsex,tbirthday from teacher

求学生

    >select sname,ssex,sbirthday from student;

加一块 union

    > select tname,tsex,tbirthday from teacher union select sname,ssex,sbirthday from student;

取别名（因加两部分加一起字段还是只是一方的，所以整体给字段起个别名）

    >select tname as name,tsex as sex,tbirthday as birthday from teacher union select sname,ssex,sbirthday from student;

（30）查询所有“女”教师和‘女"同学的name、sex、和birthday

   > select tname as name,tsex as sex,tbirthday as birthday from teacher where tsex ='女' union select sname,ssex,sbirthday from student where ssex ='女';

—分析—

查询所有“女”教师的name、sex、和birthday

    >select tname,tsex,tbirthday from teacher where tsex ='女';

查询所有“女”同学的name、sex、和birthday

    >select sname,ssex,sbirthday from student where ssex ='女';

加在一起  union

    >select tname,tsex,tbirthday from teacher where tsex ='女' union select sname,ssex,sbirthday from student where ssex ='女';

取别名

    > select tname as name,tsex as sex,tbirthday as birthday from teacher where tsex ='女' union select sname,ssex,sbirthday from student where ssex ='女';

（31）查询成绩比该课程平均成绩低的同学的成绩表

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

—分析—

查看score表

 

将表分为a、b两个表，如下：（脑子里琢磨）

 

b表用于计算平均成绩再与a表进行比较查询满足条件的

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

（32）查询所有任课教师的tname、depart

  >select tname,depart from teacher where tno in (select tno from course);

—分析—

任课 （查询教师的tno必须在course中有才满足）

    >select tname,depart from teacher where tno in (select tno from course);

（33）查询至少有两名男生的班号

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

查询班号必须要分组（group by）

男生  where……

至少有两名 （后接条件：having ）数量的话需要用到count

（34）查询student表中，不姓王“王”的同学记录

       > select * from student where sname not like'王%';

（35）查询student表中每个同学的姓名和年龄

    >select sname,year(now()) - year(sbirthday) as age from student;

—分析—

当前年份

    >select year(now());

查询每个同学的出生年份

    >select year(sbirthday) from student;

用当前年份 -  出生年份=年龄（as取别名）

>select sname,year(now()) - year(sbirthday) as age from student;

（36）查询student表中最大和最小的sbirthday值

max、min

    >select max(sbirthday) as '最大生日',min(sbirthday) as '最小生日' from student;

（37）以班号和年龄从大到小的顺序查询student表中的全部记录

    > select * from student order by class desc,sbirthday asc;

（38）查询“男”教师及其所上的课程

    > select * from course where tno in(select tno from teacher where tsex = '男');

—分析—

先取出男教师的tno

    >select tno from teacher where tsex = '男';

再从表course中取出满足上述tno的记录

    > select * from course where tno in(select tno from teacher where tsex = '男');

（39）查询最高分同学的sno、cno和degree

    > select * from score where degree=( select max(degree) from score);

—分析—

先求出最高分

    > select max(degree) from score;

求等于最高分的记录

    > select * from score where degree=( select max(degree) from score);

（40）查询和“李军”同性别的所有同学的sname

    >select sname from student where ssex =( select ssex from student where sname = '李军');

—分析—

先查出李军的性别

    > select ssex from student where sname = '李军';

查询与满足上述性别的同学的名字

    >select sname from student where ssex =( select ssex from student where sname = '李军');

（41）查询和“李军”同性别并同班的同学的sname

    >select sname from student where ssex =( select ssex from student where sname = '李军') and class=(select class from student where sname = '李军');

—分析—

先查出李军的性别

    > select ssex from student where sname = '李军';

查出李军的班级

    >select class from student where sname = '李军';

将上述两个条件连起来

    >select sname from student where ssex =( select ssex from student where sname = '李军') and class=(select class from student where sname = '李军');

（42）查询所有选修“计算机导论”课程的“男”同学的成绩表

    >select * from score where cno in(select cno from course where cname ="计算机导论") and sno in(select sno from student where ssex ='男');

—分析—

从course中查询计算机导论的cno

    >select cno from course where cname ="计算机导论";

从student表中选出男同学的sno

    >select sno from student where ssex ='男';

从score中查询满足上述两个条件的同学的记录

    >select * from score where cno in(select cno from course where cname ="计算机导论") and sno in(select sno from student where ssex ='男');

（43）、假设创建一个grade表，如下：

    >create table grade(

    ->  low int(3),

    ->  high int(3),

    -> grade char(1));

——添加数据

    >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');

问题：查询所有同学的sno、cno、grade

    >select sno,cno,grade from score,grade where degree between low and high;

—分析—

用between…and…将score表与grade表连接起来

    >select sno,cno,grade from score,grade where degree between low and high;

 

【总结，比较生疏的】

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

having count()>/

con like    以……开头的

 

　　　　

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