Mysql学生表常用操作（3）

1.题目

学生选课系统
1. 创建学生选课系统
2. 切换数据库
3. 创建学生表 TbStudent
    主键stuid ，姓名stuname，
    性别stusex，生日stubirth，电话stutel，住址stuaddr
    照片stuphoto（以二进制存）
4. 创建课程表TbCourse
主键cosid， 班级名称cosname，学分coscredit，课程描述cosintro
5. 学生选课记录表TbSC
主键scid，学生外键sid ，班级外键cid，创建日期scdate， 分数score

2.创建学生数据库

create database student;

use student;

-- 创建学生表
create table tbstudent 
( 
stuid integer not null,
stuname varchar(20) not null,
stusex bit default 1,
stubirth datetime not null,
stutel varchar(11),
stuaddr varchar(255),
stuphoto  longblob,
primary key (stuid)
);

-- 如果TBCourse已经存在就删除它
drop table if exists TbCourse;

-- 创建课程表
create table TbCourse
(
cosid integer not null,
cosname varchar(50) not null,
coscredit tinyint not null,
cosintro varchar(255)
);

-- 给课程表指定主键
alter table TbCourse add constraint pk_course primary key (cosid);

-- 创建学生选课记录表
create table tbSC 
(
scid integer primary key auto_increment,
sid integer not null,
cid integer,
scdate datetime not null,
score float
);

-- 给表TBSC添加外键约束
alter table TbSC add constraint fk_sid foreign key (sid) references TbStudent (
stuid) on delete cascade on update cascade;
alter table TbSC add constraint fk_cid foreign key (cid) references TBCourse (
cosid) on delete set null on update cascade;

3.添加数据

-- 添加学生记录
insert into TBStudent values (1001, '张三丰', default, '1978-1-1', '12345678907','成都市一环路西二段17号', null);
insert into TBStudent (stuid, stuname, stubirth) values (1002, '郭靖', '1980-2-2');
insert into TBStudent (stuid, stuname, stusex, stubirth, stuaddr) values (1003, '黄蓉', 0, '1982-3-3', '成都市二环路南四段123号');
insert into TbStudent values (1004, '张无忌', 1, '1990-4-4', null, null, null);
insert into TBStudent values
(1005, '丘处机',1, '1983-5-5', '12345678907', '北京市海淀区宝盛北里西区34号', null),
(1006, '王处一',1, '1985-6-6', '12345678906','深圳市海淀区宝盛北里西区34号', null),
(1007, '刘处玄',1, '1987-7-7', '12345678904','郑州市海淀区宝盛北里西区34号', null),
(1008, '孙不二',0, '1989-8-8', '12345678903','武汉市海淀区宝盛北里西区34号', null),
(1009, '平一指',1, '1992-9-9', '12345678902','西安海淀区宝盛北里西区34号', null),
(1010, '老不死',1, '1993-10-10', '12345678901','广州市海淀区宝盛北里西区34号', null),
(1011, '王大锤',0, '1994-11-11', '12345678917',null, null),
(1012, '隔壁老王',1, '1995-12-12', '12345678207',null, null),
(1013, '郭啸天',1, '1977-10-25', '12345678922',null, null);


-- 添加课程记录
insert into TbCourse values
(1111, 'C语言程序设计',3, '大神级讲师授课需要抢座'),
(2222, 'java程序设计', 3, null),
(3333, '数据库概论', 2, null),
(4444, '操作系统原理', 4, null);


-- 添加学生选课记录
insert into tbSC values
(default, 1001, 1111, '2016-9-1', 95),
(default, 1002, 1111, '2016-9-1', 95),
(default, 1001, 2222, now(), 95),
(default, 1001, 3333, '2017-3-1', 85),
(default, 1001, 4444, now(), null),
(default, 1002, 4444, now(), null),
(default, 1003, 2222, now(), null),
(default, 1003, 3333, now(), null),
(default, 1005, 2222, now(), null),
(default, 1006, 1111, now(), null),
(default, 1006, 2222, '2017-3-1', null),
(default, 1006, 3333, now(), null),
(default, 1006, 4444, now(), null),
(default, 1007, 1111, '2016-9-1', null),
(default, 1007, 3333, now(), null),
(default, 1007, 4444, now(), null),
(default, 1008, 2222, now(), null),
(default, 1010, 1111, now(), null);

4.对数据库的操作

-- 查询所有学生信息
select * from TbStudent;


-- 查询所有课程名称及学分(投影和别名)
select cosname as `课程名称`, coscredit as `学分` from TbCourse;


-- 查询所有女学生的姓名和出生日期(筛选)
select stuname, stubirth from TbStudent where stusex=0;


-- 查询所有80后学生的姓名、性别和出生日期(筛选)
select stuname as `姓名`, if(stusex, '男', '女') as `性别`, stubirth as `出生日期`
from TbStudent where stubirth between '1980-1-1' and '1989-12-31';


-- 查询姓王的学生姓名和性别(模糊)
select stuname, stusex from TbStudent where stuname like '王%';


-- 查询姓郭名字总共两个字的学生的姓名(模糊)
select stuname from TbStudent where stuname like '郭_';


-- 查询姓郭名字总共三个字的学生的姓名(模糊)
select stuname from TbStudent where stuname like '郭__';


-- 查询名字中有王字的学生的姓名(模糊)
select stuname from TbStudent where stuname like '%王%';


-- 查询没有录入家庭住址和照片的学生姓名(多条件筛选和空值处理)
select stuname from TbStudent where stuaddr is null and stuphoto is null;


-- 查询学生选课的所有日期(去重)
select distinct scdate from TbSC;


-- 查询学生的姓名和生日按年龄从大到小排列(排序)
select stuname, stubirth from TbStudent order by stubirth;


-- 查询所有录入了家庭住址的男学生的姓名、出生日期和家庭住址按年龄从小到大排列(多条件筛选和排序)
select stuname, stubirth, stuaddr from TbStudent where stusex=1 and stuaddr is not null order by stubirth desc;


-- 查询年龄最大的学生的出生日期(聚合函数)
select min(stubirth) from TbStudent;


-- 查询年龄最小的学生的出生日期(聚合函数)
select max(stubirth) from TbStudent;


-- 查询男女学生的人数(分组和聚合函数)
select if(stusex, '男', '女') as `性别`, count(stusex) as `人数` from TbStudent group by stusex;


-- 查询课程编号为1111的课程的平均成绩(筛选和聚合函数)
select avg(score) as `平均成绩` from TbSC where cid=1111;


-- 查询学号为1001的学生所有课程的总成绩(筛选和聚合函数)
select sum(score) as `总成绩` from TbSC where sid=1001;


-- 查询每个学生的学号和平均成绩, null值处理成0(分组和聚合函数)
select sid as `学号`, ifnull(avg(score), 0) as `平均成绩` from TbSC 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
select sid as `学号`, avg(score) as `平均成绩` from TbSC group by sid having avg(score)>=90;


-- 查询年龄最大的学生的姓名(子查询)
select stuname from TbStudent where stubirth=(select min(stubirth) from TbStudent);


-- 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)
select stuname from TbStudent where stuid in 
(select sid from TbSC group by sid having count(sid)>2);


-- 查询选课学生的姓名和平均成绩(子查询和连接查询)
-- 写法1:
select stuname, avgscore from TbStudent t1 inner join
(select sid, avg(score) as avgscore from TbSC where score is not null group by sid) t2
on t1.stuid=t2.sid;
-- 写法2: 
select stuname, avgscore from TbStudent t1,
(select sid, avg(score) as avgscore from TbSC where score is not null group by sid) t2
where t1.stuid=t2.sid;


-- 查询学生姓名、所选课程名称和成绩(连接查询)
-- 写法1:
select stuname, cosname, score from 
TbStudent t1, TbCourse t2, TbSC t3
where t1.stuid=t3.sid and t2.cosid=t3.cid and t3.score is not null;
-- 写法2:
select stuname, cosname, score from TbStudent t1 inner join TbCourse t2
inner join (select sid, cid, score from TbSC where score is not null) t3 
on t1.stuid=t3.sid and t2.cosid=t3.cid;


-- 查询每个学生的姓名和选课数量(左外连接和子查询)
select stuname as `姓名`, ifnull(coscount, 0) as `选课数` from TbStudent t1
left outer join (select sid, count(sid) as coscount from TbSC group by sid) t2 
on t1.stuid=t2.sid;