MySQL基础练习50题
题目来源：https://link.zhihu.com/?target=http%3A//blog.csdn.net/flycat296/article/details/63681089
一、练习所使用的表格格式如下：
1. Student 表
Student(SId,Sname,Sage,Ssex) # 其中 SId 表示学生编号,Sname 表示学生姓名,Sage 表示出生年月,Ssex 表示学生性别；
2. Course 表
Course(CId,Cname,TId) # 其中 CId 表示课程编号,Cname 表示课程名称,TId 表示教师编号；
3. Teacher 表
Teacher(TId,Tname) # 其中 TId 表示教师编号,Tname 表示教师姓名；
4. SC (成绩)表
SC(SId,CId,score) # 其中 SId 表示学生编号,CId 表示课程编号,score 表示分数。
二、练习所使用的数据如下：
1. Student 表
create table Student(SId varchar(10),Sname varchar(10),Sage datetime,Ssex varchar(10));
insert into Student values('01' , '赵雷' , '1990-01-01' , '男');
insert into Student values('02' , '钱电' , '1990-12-21' , '男');
insert into Student values('03' , '孙风' , '1990-05-20' , '男');
insert into Student values('04' , '李云' , '1990-08-06' , '男');
insert into Student values('05' , '周梅' , '1991-12-01' , '女');
insert into Student values('06' , '吴兰' , '1992-03-01' , '女');
insert into Student values('07' , '郑竹' , '1989-07-01' , '女');
insert into Student values('09' , '张三' , '2017-12-20' , '女');
insert into Student values('10' , '李四' , '2017-12-25' , '女');
insert into Student values('11' , '李四' , '2017-12-30' , '女');
insert into Student values('12' , '赵六' , '2017-01-01' , '女');
insert into Student values('13' , '孙七' , '2018-01-01' , '女');2. Course 表
create table Course(CId varchar(10),Cname nvarchar(10),TId varchar(10));
insert into Course values('01' , '语文' , '02');
insert into Course values('02' , '数学' , '01');
insert into Course values('03' , '英语' , '03');3. Teacher 表
create table Teacher(TId varchar(10),Tname varchar(10));
insert into Teacher values('01' , '张三');
insert into Teacher values('02' , '李四');
insert into Teacher values('03' , '王五');4. SC 表
create table SC(SId varchar(10),CId varchar(10),score decimal(18,1));
insert into SC values('01' , '01' , 80);
insert into SC values('01' , '02' , 90);
insert into SC values('01' , '03' , 99);
insert into SC values('02' , '01' , 70);
insert into SC values('02' , '02' , 60);
insert into SC values('02' , '03' , 80);
insert into SC values('03' , '01' , 80);
insert into SC values('03' , '02' , 80);
insert into SC values('03' , '03' , 80);
insert into SC values('04' , '01' , 50);
insert into SC values('04' , '02' , 30);
insert into SC values('04' , '03' , 20);
insert into SC values('05' , '01' , 76);
insert into SC values('05' , '02' , 87);
insert into SC values('06' , '01' , 31);
insert into SC values('06' , '03' , 34);
insert into SC values('07' , '02' , 89);
insert into SC values('07' , '03' , 98);三、题目、答案以及截图如下：
01. 查询 "01" 课程比 "02" 课程成绩高的学生的信息及课程分数。
select t1.SId,t1.Sname,t1.Sage,t1.Ssex,t2.CId,t2.score,t3.CId,t3.score from
(select SId,Sname,Sage,Ssex from Student) as t1,
(select SId,CId,score from SC) as t2,
(select SId,CId,score from SC) as t3
where t1.SId=t2.SId and t1.SId=t3.SId and t2.CIdt3.score; 
02. 查询平均成绩大于等于 60 分的同学的学生编号和学生姓名和平均成绩。
select t2.SId,t2.Sname,avgscore from
(select SId,AVG(score) as avgscore from sc
GROUP BY SId having AVG(score)>60) as t1,
(select * from Student) as t2
where t1.SId=t2.SId; 
03. 查询在 SC 表存在成绩的学生信息
select Distinct student.*
from student,sc
where student.SId=sc.SId; 
4.查询所有同学的学生编号、学生姓名、选课总数、所有课程的总成绩(没成绩的显示为null)
select student.SId,student.Sname,t1.sumscore,t1.coursecount from student,
(select SC.SId,sum(sc.score) as sumscore,count(sc.CId) as coursecount
from sc group by sc.sid) as t1
where student.Sid=t1.sid;
05. 查询「李」姓老师的数量
select count(*)
from Teacher
where Teacher.Tname like '李%'; 
06. 查询学过「张三」老师授课的同学的信息
/* 方法一 */
select student.* from student,
(select sc.Sid from sc,
(select course.CId from course,teacher
where course.TId=teacher.TId and teacher.Tname='张三') as t1
where sc.cid=t1.cid) as t2
where t2.Sid=student.Sid;
/* 方法二 */
select student.*
from teacher ,course ,student,sc
where teacher.Tname='张三'
and teacher.TId=course.TId
and course.CId=sc.CId
and sc.SId=student.SId
07. 查询没有学全所有课程的同学的信息
（未完待续，如果各位有发现错误或者更好的解决方案，欢迎指教）