mysql 多表联合查询 简单演示

数据导入(方便测试)

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' , '1990-12-20' , '男');
insert into Student values('04' , '李云' , '1990-12-06' , '男');
insert into Student values('05' , '周梅' , '1991-12-01' , '女');
insert into Student values('06' , '吴兰' , '1992-01-01' , '女');
insert into Student values('07' , '郑竹' , '1989-01-01' , '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' , '2012-06-06' , '女');
insert into Student values('12' , '赵六' , '2013-06-13' , '女');
insert into Student values('13' , '孙七' , '2014-06-01' , '女');

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');

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');

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);

题目以及sql语句

1. 查询两门及其以上不及格课程的同学的学号，姓名及其平均成绩

select A.Sname, B.* from Student as A inner join (select SId, round(avg(score), 2) as avg_score from SC where score < 60 group by SId having count(*) > 1) as B on A.SId=B.SId;

注意点:(聚合函数要取别名!!!)

2. 检索" 01 "课程分数小于 60，按分数降序排列的学生信息

select * from Student where SId in (select SId from SC group by CId, score, SId having CId = 1 and score < 60 order by score desc);

3. 按平均成绩从高到低显示所有学生的所有课程的成绩以及平均成绩

select A.*, B.avg_score from Student as A inner join (select SId, round(avg(score), 2) as avg_score from SC group by SId) as B on A.SId=B.SId  order by B.avg_score desc;

4. 查询 1990 年出生的学生名单

select * from Student where date(Sage) >= '1990-01-01 00:00:00' and date(Sage) < '1991-01-01 00:00:00';

5. 查询每门课程的平均成绩，结果按平均成绩降序排列，平均成绩相同时，按课程编号升序排列

select A.CId, A.Cname, B.avg_score from Course as A inner join (select CId, round(avg(score), 2) as avg_score from SC group by CId) as B on A.CId=B.CId order by B.avg_score desc, B.CId;

6. 查询平均成绩大于等于 85 的所有学生的学号、姓名和平均成绩

select * from Student as A inner join (select sc.SId, round(avg(sc.score), 2) from SC as sc group by SId having avg(score) >= 85) as B on A.SId=B.SId;

7. 查询本月过生日的学生

select * from Student where month(Sage) = month(curdate());

8. 查询名字中含有「风」字的学生信息

select * from Student where Sname like('%风%');

9. 查询各科成绩最高分、最低分和平均分

select A.Cname, B.* from Course as A inner join (select CId, max(score), min(score), round(avg(score), 2) from SC group by CId) as B on A.CId=B.CId;

若有错误, 烦请纠正。