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数据库表名和字段设计
1.学生表
Student(s_id,s_name,s_birth,s_sex)
学生编号,学生姓名, 出生年月,学生性别
2.课程表
Course(c_id,c_name,t_id)
课程编号, 课程名称, 教师编号
3.教师表
Teacher(t_id,t_name)
教师编号,教师姓名
4.成绩表
Score (s_id,c_id,s_score)
学生编号,课程编号,分数
建表语句
学生表
CREATE TABLE `Student`( `s_id` VARCHAR(20), `s_name` VARCHAR(20) NOT NULL DEFAULT '', `s_birth` VARCHAR(20) NOT NULL DEFAULT '', `s_sex` VARCHAR(10) NOT NULL DEFAULT '', PRIMARY KEY(`s_id`) );课程表
CREATE TABLE `Course`( `c_id` VARCHAR(20), `c_name` VARCHAR(20) NOT NULL DEFAULT '', `t_id` VARCHAR(20) NOT NULL, PRIMARY KEY(`c_id`) ); 教师表
CREATE TABLE `Teacher`( `t_id` VARCHAR(20), `t_name` VARCHAR(20) NOT NULL DEFAULT '', PRIMARY KEY(`t_id`) );成绩表
CREATE TABLE `Score`( `s_id` VARCHAR(20), `c_id` VARCHAR(20), `s_score` INT(3), PRIMARY KEY(`s_id`,`c_id`) ); 插入测试数据
学生表
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('08' , '王菊' , '1990-01-20' , '女'); 教师表
insert into Course values('01' , '语文' , '02');
insert into Course values('02' , '数学' , '01');
insert into Course values('03' , '英语' , '03'); 课程表
insert into Teacher values('01' , '张三');
insert into Teacher values('02' , '李四');
insert into Teacher values('03' , '王五'); 成绩表
insert into Score values('01' , '01' , 80);
insert into Score values('01' , '02' , 90);
insert into Score values('01' , '03' , 99);
insert into Score values('02' , '01' , 70);
insert into Score values('02' , '02' , 60);
insert into Score values('02' , '03' , 80);
insert into Score values('03' , '01' , 80);
insert into Score values('03' , '02' , 80);
insert into Score values('03' , '03' , 80);
insert into Score values('04' , '01' , 50);
insert into Score values('04' , '02' , 30);
insert into Score values('04' , '03' , 20);
insert into Score values('05' , '01' , 76);
insert into Score values('05' , '02' , 87);
insert into Score values('06' , '01' , 31);
insert into Score values('06' , '03' , 34);
insert into Score values('07' , '02' , 89);
insert into Score values('07' , '03' , 98); 常见题目
1、查询"01"课程比"02"课程成绩高的学生的信息及课程分数
select a.*,b.s_score as 01_score,c.s_score as 02_score from
student ajoin score b on a.s_id=b.s_id and b.c_id='01'left join score c on a.s_id=c.s_id and c.c_id='02' or c.c_id = null whereb.s_score>c.s_score;2、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 b.s_id,b.s_name,ROUND(AVG(a.s_score),2) as avg_score fromstudent bjoin score a on b.s_id = a.s_idGROUP BY b.s_id,b.s_name HAVING avg_score >= 60;3、查询平均成绩小于60分的同学的学生编号和学生姓名和平均成绩-- (包括有成绩的和无成绩的)
select b.s_id,b.s_name,ROUND(AVG(a.s_score),2) as avg_score fromstudent bleft join score a on b.s_id = a.s_idGROUP BY b.s_id,b.s_name HAVING avg_score < 60union
select a.s_id,a.s_name,0 as avg_score from student awhere a.s_id not in (select distinct s_id from score);4、查询学过"张三"老师授课的同学的信息
select a.* fromstudent ajoin score b on a.s_id=b.s_id where b.c_id in(select c_id from course where t_id = (select t_id from teacher where t_name = '张三'));5、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
select a.s_id,a.s_name,count(b.c_id) as sum_course,sum(b.s_score) as sum_score from student aleft join score b on a.s_id = b.s_idGROUP BY a.s_id,a.s_name;6、查询学过编号为"01"并且也学过编号为"02"的课程的同学的信息
select a.* fromstudent a,score b,score cwhere a.s_id = b.s_id and a.s_id = c.s_id and b.c_id ='01' and c.c_id='02';7、查询学过编号为"01"但是没有学过编号为"02"的课程的同学的信息
select a.* fromstudent awhere a.s_id in (select s_id from score where c_id='01') and a.s_id not in (select s_id from score where c_id='02');