练习内容：主要针对学生选课系统而设计，其中设计到三张表，分别为学生表，课程表，学生和课程对应的关联表。
学生表主要用于存储学生信息，包括姓名，性别，地址，电话等信息
课程表主要用于存储课程的信息，包括课程的名称，课程的描述，学分等信息
关联表，用于关联学生表和课程表，课程的分数等
表创建/数据准备
show databases;drop database if exists SRS;create database SRS default charset utf8;use SRS;show tables;create table TbStudent ( stuid integer not null, stuname varchar(20) not null, stusex bit default 1, stubirth datetime not null, stutel char(11), stuaddr varchar(255), stuphoto longblob, primary key (stuid) );alter table TbStudent drop column stutel;desc TbStudent;drop table if exists TbCourse;create table TbCourse ( cosid integer not null, cosname varchar(50) not null, coscredit tinyint not null, cosintro varchar(255) );alter table TbCourse add constraint pk_course primary key (cosid);create table TbSC ( scid integer primary key auto_increment, sid integer not null, cid integer, scdate datetime not null, score float );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;insert into TbStudent values (1001, '张三丰', default, '1978-1-1', '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); insert into TbStudent values (1005, '丘处机', 1, '1983-5-5', '北京市海淀区宝盛北里西区28号', null), (1006, '王处一', 1, '1985-6-6', '深圳市宝安区宝安大道5010号', null), (1007, '刘处玄', 1, '1987-7-7', '郑州市金水区纬五路21号', null), (1008, '孙不二', 0, '1989-8-8', '武汉市光谷大道61号', null), (1009, '平一指', 1, '1992-9-9', '西安市雁塔区高新六路52号', null), (1010, '老不死', 1, '1993-10-10', '广州市天河区元岗路310号', null); (1011, '王大锤', 0, '1994-11-11', null, null), (1012, '隔壁老王', 1, '1995-12-12', null, null), (1013, '郭啸天', 1, '1977-10-25', null, null);delete from TbStudent where stuid=1004;update TbStudent set stubirth='1980-12-12', stuaddr='上海市宝山区同济支路199号' where stuid=1002;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', 94), (default, 1001, 2222, now(), null), (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', 80), (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);题目练习
1、查询所有学生信息
select * from TbStudent;2、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;3、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;4、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';5、查询姓王的学生姓名和性别(模糊)
select stuname, stusex from TbStudent where stuname like '王%';6、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_';7、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__';8、查询名字中有王字的学生的姓名(模糊)
select stuname from TbStudent where stuname like '%王%';9、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;10、查询学生选课的所有日期(去重)
select distinct scdate from TbSC;11、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;12、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;13、查询年龄最大的学生的出生日期(聚合函数)
select min(stubirth) from TbStudent;14、查询年龄最小的学生的出生日期(聚合函数)
select max(stubirth) from TbStudent;15、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;16、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;17、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;18、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;19、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;20、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);21、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);22、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;23、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;24、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;