MySQL习题

MySQL习题

school数据库操作

– 如果存在名为school的数据库就删除它

drop database if exists school;

– 创建名为school的数据库并设置默认的字符集

create database school default charset utf8mb4;

– 切换到school数据库上下文环境

use school;

– 创建学院表

create table tb_college
(
collid 		int auto_increment comment '编号',
collname 	varchar(50) not null comment '名称',
collintro 	varchar(500) default '' comment '介绍',
primary key (collid)
);

– 修改学院表给学院名称列添加唯一性约束

alter table tb_college add constraint un_college_name unique (collname);

– 创建学生表

create table tb_student
(
stuid 		int not null comment '学号',
stuname 	varchar(20) not null comment '姓名',
stusex 		boolean default 1 comment '性别',
stubirth 	date not null comment '出生日期',
stuaddr 	varchar(255) default '' comment '籍贯',
collid 		int not null comment '所属学院',
primary key (stuid),
foreign key (collid) references tb_college (collid)
);

– 创建教师表

create table tb_teacher
(
teaid 		int not null comment '工号',
teaname 	varchar(20) not null comment '姓名',
teatitle 	varchar(10) default '讲师' comment '职称',
collid 		int not null comment '所属学院',
primary key (teaid),
foreign key (collid) references tb_college (collid)
);

– 创建课程表

create table tb_course
(
couid 		int not null comment '编号',
couname 	varchar(50) not null comment '名称',
coucredit 	int not null comment '学分',
teaid 		int not null comment '授课老师',
primary key (couid),
foreign key (teaid) references tb_teacher (teaid)
);

– 创建选课记录表

create table tb_record
(
recid 		int auto_increment comment '选课记录编号',
sid 		int not null comment '选课学生',
cid 		int not null comment '所选课程',
seldate 	datetime not null comment '选课时间日期',
score 		decimal(4,1) comment '考试成绩',
primary key (recid),
foreign key (sid) references tb_student (stuid),
foreign key (cid) references tb_course (couid),
unique (sid, cid)
);

– 插入学院数据

insert into tb_college (collname, collintro) values 
('计算机学院', '计算机学院1958年设立计算机专业，1981年建立计算机科学系，1998年设立计算机学院，2005年5月，为了进一步整合教学和科研资源，学校决定，计算机学院和软件学院行政班子合并统一运作、实行教学和学生管理独立运行的模式。 学院下设三个系：计算机科学与技术系、物联网工程系、计算金融系；两个研究所：图象图形研究所、网络空间安全研究院（2015年成立）；三个教学实验中心：计算机基础教学实验中心、IBM技术中心和计算机专业实验中心。'),
('外国语学院', '外国语学院设有7个教学单位，6个文理兼收的本科专业；拥有1个一级学科博士授予点，3个二级学科博士授予点，5个一级学科硕士学位授权点，5个二级学科硕士学位授权点，5个硕士专业授权领域，同时还有2个硕士专业学位（MTI）专业；有教职员工210余人，其中教授、副教授80余人，教师中获得中国国内外名校博士学位和正在职攻读博士学位的教师比例占专任教师的60%以上。'),
('经济管理学院', '经济学院前身是创办于1905年的经济科；已故经济学家彭迪先、张与九、蒋学模、胡寄窗、陶大镛、胡代光，以及当代学者刘诗白等曾先后在此任教或学习。');

– 插入学生数据

insert into tb_student (stuid, stuname, stusex, stubirth, stuaddr, collid) 
values
    (1001, '杨逍', 1, '1990-3-4', '四川成都', 1),
    (1002, '任我行', 1, '1992-2-2', '湖南长沙', 1),
    (1033, '王语嫣', 0, '1989-12-3', '四川成都', 1),
    (1572, '岳不群', 1, '1993-7-19', '陕西咸阳', 1),
    (1378, '纪嫣然', 0, '1995-8-12', '四川绵阳', 1),
    (1954, '林平之', 1, '1994-9-20', '福建莆田', 1),
    (2035, '东方不败', 1, '1988-6-30', null, 2),
    (3011, '林震南', 1, '1985-12-12', '福建莆田', 3),
    (3755, '项少龙', 1, '1993-1-25', null, 3),
    (3923, '杨不悔', 0, '1985-4-17', '四川成都', 3),
    (4040, '炼腰的隔壁老王', 1, '1989-1-1', '四川成都', 2);

– 删除学生数据

delete from tb_student where stuid=4040;

– 更新学生数据

update tb_student set stuname='杨过', stuaddr='湖南长沙' where stuid=1001;

– 插入老师数据

insert into tb_teacher (teaid, teaname, teatitle, collid) values 
(1122, '张三丰', '教授', 1),
(1133, '宋远桥', '副教授', 1),
(1144, '杨逍', '副教授', 1),
(2255, '范遥', '副教授', 2),
(3366, '韦一笑', default, 3);

– 插入课程数据

insert into tb_course (couid, couname, coucredit, teaid) values 
(1111, 'Python程序设计', 3, 1122),
(2222, 'Web前端开发', 2, 1122),
(3333, '操作系统', 4, 1122),
(4444, '计算机网络', 2, 1133),
(5555, '编译原理', 4, 1144),
(6666, '算法和数据结构', 3, 1144),
(7777, '经贸法语', 3, 2255),
(8888, '成本会计', 2, 3366),
(9999, '审计学', 3, 3366);

– 插入选课数据

insert into tb_record (sid, cid, seldate, score) values 
(1001, 1111, '2017-09-01', 95),
(1001, 2222, '2017-09-01', 87.5),
(1001, 3333, '2017-09-01', 100),
(1001, 4444, '2018-09-03', null),
(1001, 6666, '2017-09-02', 100),
(1002, 1111, '2017-09-03', 65),
(1002, 5555, '2017-09-01', 42),
(1033, 1111, '2017-09-03', 92.5),
(1033, 4444, '2017-09-01', 78),
(1033, 5555, '2017-09-01', 82.5),
(1572, 1111, '2017-09-02', 78),
(1378, 1111, '2017-09-05', 82),
(1378, 7777, '2017-09-02', 65.5),
(2035, 7777, '2018-09-03', 88),
(2035, 9999, curdate(), null),
(3755, 1111, curdate(), null),
(3755, 8888, curdate(), null),
(3755, 9999, '2017-09-01', 92);

– 查询所有学生的信息

select * from tb_student;

select stuid, stuname, stusex, stubirth, stuaddr, collid from tb_student;

– 查询所有课程名称及学分(投影和别名)

select couname as 课程名称, coucredit as 学分 from tb_course;

– 查询所有学生的姓名和性别

select stuname as 姓名, case stusex when 1 then '男' else '女' end as 性别 from tb_student;

– if函数并不是标准SQL的部分，而是MySQL特有的函数，如果换成其他数据库，
– 下面的查询可能不能成立，例如在Oracle中，实现同样功能的函数叫decode。

select stuname as 姓名, if(stusex, '男', '女') as 性别 from tb_student;

– 查询所有老师的姓名和职称

select teaname, teatitle from tb_teacher;

– 查询所有女学生的姓名和出生日期(筛选)

select stuname, stubirth from tb_student where stusex=0;

– 查询所有80后学生的姓名和出生日期(筛选)
– 在执行筛选操作时，如果有多个条件，可以通过and和or关键字进行组合，
– 也可以使用not将条件变成其对立面（逻辑变反）。

select stuname, stubirth from tb_student where stubirth>='1980-1-1' and stubirth<='1989-12-31';

select stuname, stubirth from tb_student where stubirth between '1980-1-1' and '1989-12-31';

– 查询姓“杨”的学生姓名和性别(模糊)

select stuname, stusex from tb_student where stuname like '杨%';

– 查询姓“杨”名字两个字的学生姓名和性别(模糊)

select stuname, stusex from tb_student where stuname like '杨_';

– 查询姓“杨”名字三个字的学生姓名和性别(模糊)

select stuname, stusex from tb_student where stuname like '杨__';

– 查询名字中有“不”字或“嫣”字的学生的姓名(模糊)

select stuname from tb_student where stuname like '%不%' or stuname like '%嫣%';

select stuname from tb_student where stuname like '%不%'
union
select stuname from tb_student where stuname like '%嫣%';

– 查询没有录入家庭住址的学生姓名(空值)
– 在SQL中，null跟任何数据做任何运算结果都是null，而null值相当于布尔值的假（不成立）
– select stuname from tb_student where 1>2;
– select stuname from tb_student where stuaddr=null;

select stuname from tb_student where stuaddr<=>null;
select stuname from tb_student where stuaddr is null;

– 查询录入了家庭住址的学生姓名(空值)
– select stuname from tb_student where stuaddr<>null;

select stuname from tb_student where stuaddr is not null;

– 查询学生选课的所有日期(去重)

select distinct seldate from tb_record;

– 查询学生的家庭住址(去重)

select distinct stuaddr from tb_student where stuaddr is not null;

– 查询男学生的姓名和生日按年龄从大到小排列(排序)
– order by可以实现根据指定的字段排序，asc - 升序，desc - 降序

select stuname, stubirth from tb_student where stusex=1 order by stubirth;

– curdate()：获取当前日期
– datediff()：计算两个日期相差多少天
– floor()：下取整（取不超过指定数值的最大的整数）

select stuname, floor(datediff(curdate(), stubirth)/365) as age from tb_student where stusex=1 order by age desc;

– max() / min() / avg() / sum() / count()
– 查询年龄最大的学生的出生日期(聚合函数)

select min(stubirth) from tb_student;

– 查询年龄最小的学生的出生日期(聚合函数)

select max(stubirth) from tb_student;

– 查询男女学生的人数(分组和聚合函数)

select stusex, count(stuid) as total from tb_student group by stusex order by total desc;

– 查询课程编号为1111的课程的平均成绩(筛选和聚合函数)
– 在使用聚合函数的时候null值自动被忽略

select avg(score) from tb_record where cid=1111;

– 查询有多少个学生选了编号为1111的课程

select count(sid) from tb_record where cid=1111;

– 查询有多少个学生参加了编号为1111的课程的考试并获得了成绩

select count(score) from tb_record where cid=1111;

– 查询编号为1111的课程的最高分

select max(score) from tb_record where cid=1111;

– 查询编号为1111的课程的最低分

select min(score) from tb_record where cid=1111;

– 查询学号为1001的学生所有课程的平均分(筛选和聚合函数)

select avg(score) from tb_record where sid=1001;

– 查询每个学生的学号和平均成绩(分组和聚合函数)

select sid, round(avg(score), 1) as avgscore from tb_record group by sid;

– 查询平均成绩大于等于90分的学生的学号和平均成绩(分组后的数据筛选)
– 分组之前的筛选使用where子句，分组之后的筛选使用having子句！！！

select sid, round(avg(score), 1) as avgscore from tb_record group by sid having avgscore>=90;

– 查询年龄最大的学生的姓名(嵌套查询/子查询)
– 嵌套查询：把一个查询的结果作为另外一个查询的一部分来使用，也叫子查询。

select stuname from tb_student where stubirth=(select min(stubirth) from tb_student);

– 查询年龄最小的学生姓名和年龄(子查询+运算)

select stuname, floor(datediff(curdate(), stubirth)/365) as age from tb_student where stubirth=(select max(stubirth) from tb_student);

– 查询年龄最大的男学生的姓名

select stuname from tb_student where stubirth=(select min(stubirth) from tb_student where stusex=1) and stusex=1;

– 查询选了两门以上的课程的学生姓名(子查询/分组条件/集合运算)
– in / not in 判断元素在不在集合中的成员运算

select stuname from tb_student where stuid in (select sid from tb_record group by sid having count(sid)>2);

– 查询每门课程的名称、学分和授课老师的姓名(连接查询/连表查询)
– 连接两张表的时候如果没有连接条件就会形成笛卡尔乘积（9*5=45）
– 如果两张表有同名的列，在使用这个列的时候，需要使用完全限定名（表名.列名）

select couname, coucredit, teaname from tb_course t1, tb_teacher t2 where t1.teaid=t2.teaid;

– 内连接

select couname, coucredit, teaname from tb_course t1 inner join tb_teacher t2 on t1.teaid=t2.teaid;

– 查询每个学生的姓名和平均成绩(嵌套查询+连接查询)

select stuname, avgscore from tb_student t1, (select sid, round(avg(score),1) as avgscore from tb_record group by sid) t2 where t1.stuid=t2.sid;

select stuname, avgscore from tb_student t1 inner join (select sid, round(avg(score),1) as avgscore from tb_record group by sid) t2 on t1.stuid=t2.sid;

– 查询学生姓名、课程名称以及成绩(连接查询)

select stuname, couname, score from tb_student, tb_course, tb_record where stuid=sid and couid=cid and score is not null;

select stuname, couname, score from tb_student inner join tb_record on stuid=sid inner join tb_course on couid=cid where score is not null;

– 按成绩排降序，取前5条记录

select stuname, couname, score from tb_student, tb_course, tb_record where stuid=sid and couid=cid and score is not null order by score desc limit 5;

– 按成绩排降序，取6-10条记录

select stuname, couname, score from tb_student, tb_course, tb_record where stuid=sid and couid=cid and score is not null order by score desc limit 5 offset 5;

– 按成绩排降序，取11-15条记录 —> 分页查询

select stuname, couname, score from tb_student, tb_course, tb_record where stuid=sid and couid=cid and score is not null order by score desc limit 5 offset 10;

select stuname, couname, score from tb_student, tb_course, tb_record where stuid=sid and couid=cid and score is not null order by score desc limit 10,5;

– select + from + where + group by + having + order by + limit

– 查询每个学生的姓名和选课数量(左外连接和子查询)
– 外连接：左外、右外、全外（MySQL不支持）
– 内连接：只能查出满足连表条件的记录
– 左外连接：保证左表的记录要完整的查出来，即便它并不满足连表条件，不满足连表条件的地方填充null
– 查询语句出现前面的表叫左表，出现在后面的表叫右表

select stuname, ifnull(total, 0) from tb_student t1 left join (select sid, count(sid) as total from tb_record group by sid) t2 on t1.stuid=t2.sid;

– 下面的左外连接的写法MySQL暂时不支持
/* select stuname, total from tb_student t1, (select sid, count(sid) as total from tb_record group by sid) t2 where t1.stuid=t2.sid(+); */

hrs数据库操作

drop database if exists hrs;
create database hrs default charset utf8mb4;

use hrs;

drop table if exists tb_emp;
drop table if exists tb_dept;

create table tb_dept
(
dno int not null comment '编号',
dname varchar(10) not null comment '名称',
dloc varchar(20) not null comment '所在地',
primary key (dno)
);

-- alter table tb_dept add constraint pk_dept_dno primary key(dno);

insert into tb_dept values 
	(10, '会计部', '北京'),
	(20, '研发部', '成都'),
	(30, '销售部', '重庆'),
	(40, '运维部', '深圳');

create table tb_emp
(
eno int not null comment '员工编号',
ename varchar(20) not null comment '员工姓名',
job varchar(20) not null comment '员工职位',
mgr int comment '主管编号',
sal int not null comment '员工月薪',
comm int comment '每月补贴',
dno int comment '所在部门编号',
primary key (eno),
foreign key (dno) references tb_dept(dno),
foreign key (mgr) references tb_emp(eno)
);

-- alter table tb_emp add constraint fk_emp_mgr foreign key (mgr) references tb_emp (eno);
-- alter table tb_emp add constraint fk_emp_dno foreign key (dno) references tb_dept (dno);

insert into tb_emp values 
	(7800, '张三丰', '总裁', null, 9000, 1200, 20),
	(2056, '乔峰', '分析师', 7800, 5000, 1500, 20),
	(3088, '李莫愁', '设计师', 2056, 3500, 800, 20),
	(3211, '张无忌', '程序员', 2056, 3200, null, 20),
	(3233, '丘处机', '程序员', 2056, 3400, null, 20),
	(3251, '张翠山', '程序员', 2056, 4000, null, 20),
	(5566, '宋远桥', '会计师', 7800, 4000, 1000, 10),
	(5234, '郭靖', '出纳', 5566, 2000, null, 10),
	(3344, '黄蓉', '销售主管', 7800, 3000, 800, 30),
	(1359, '胡一刀', '销售员', 3344, 1800, 200, 30),
	(4466, '苗人凤', '销售员', 3344, 2500, null, 30),
	(3244, '欧阳锋', '程序员', 3088, 3200, null, 20),
	(3577, '杨过', '会计', 5566, 2200, null, 10),
	(3588, '朱九真', '会计', 5566, 2500, null, 10);

– 查询月薪最高的员工姓名和月薪

select ename, sal from tb_emp where sal=(select max(sal) from tb_emp);

– 查询员工的姓名和年薪((月薪+补贴)*13)

select ename, (sal + ifnull(comm, 0)) * 13 as annsal from tb_emp order by annsal desc;

– 查询有员工的部门的编号和人数

select dno, count(eno) from tb_emp group by dno;

select dno, count(eno) from tb_emp group by dno having count(eno)>=5;

– 查询所有部门的名称和人数

select dname, ifnull(total, 0) as total from tb_dept t1 left join (select dno, count(eno) as total from tb_emp group by dno) t2 on t1.dno=t2.dno;

– 查询月薪最高的员工(Boss除外)的姓名和月薪

select ename, sal from tb_emp where sal=(select max(sal) from tb_emp where mgr is not null);

– 查询月薪超过平均月薪的员工的姓名和月薪

select ename, sal from tb_emp where sal>(select avg(sal) from tb_emp);

– 查询月薪超过其所在部门平均月薪的员工的姓名、部门编号和月薪

select ename, t1.dno, sal from tb_emp t1 inner join (select dno, avg(sal) as avgsal from tb_emp group by dno) t2 on t1.dno=t2.dno where sal>avgsal;

– 查询部门中薪水最高的人姓名、月薪和所在部门名称

select ename, sal, dname from tb_emp t1 inner join (select dno, max(sal) as maxsal from tb_emp group by dno) t2 on t1.dno=t2.dno inner join tb_dept t3 on t2.dno=t3.dno where sal=maxsal;

– 查询主管的姓名和职位

select ename, job from tb_emp where eno in (select distinct mgr from tb_emp where mgr is not null);

– 一般情况下写SQL的时候，尽量避免使用distinct、in、not in运算，因为它们的性能都很差
– 可以考虑使用存在性判断（exists、not exists）来替代去重和集合成员运算

select ename, job from tb_emp t1 where exists (select 'x' from tb_emp t2 where t1.eno=t2.mgr);

– select 1, ‘x’ from tb_emp;
– select now() from tb_emp;

– 查询月薪排名4~6名的员工排名、姓名和月薪

select num, ename, sal from (select @a:=@a+1 as num, ename, sal from tb_emp t1, (select @a:=0) t2 order by sal desc) t3 limit 3 offset 3;