SQL语句学习笔记
表结构：
-- 教师表
CREATE TABLE teacher(
tno INT NOT NULL PRIMARY KEY,
tname VARCHAR(20) NOT NULL
);
INSERT INTO teacher(tno,tname)VALUES(1,'张老师');
INSERT INTO teacher(tno,tname)VALUES(2,'王老师');
INSERT INTO teacher(tno,tname)VALUES(3,'李老师');
INSERT INTO teacher(tno,tname)VALUES(4,'赵老师');
INSERT INTO teacher(tno,tname)VALUES(5,'刘老师');
INSERT INTO teacher(tno,tname)VALUES(6,'向老师');
INSERT INTO teacher(tno,tname)VALUES(7,'李文静');
INSERT INTO teacher(tno,tname)VALUES(8,'叶平');
-- 学生表
CREATE TABLE student(
sno int NOT NULL PRIMARY KEY,
sname varchar(20) NOT NULL,
sage datetime NOT NULL,
ssex char(2) NOT NULL
);
INSERT INTO student(sno,sname,sage,ssex) VALUES(1,'张三','1980-1-23','男');
INSERT INTO student(sno,sname,sage,ssex) VALUES(2,'李四','1982-12-12','男');
INSERT INTO student(sno,sname,sage,ssex) VALUES(3,'张飒','1981-9-9','男');
INSERT INTO student(sno,sname,sage,ssex) VALUES(4,'莉莉','1983-3-23','女');
INSERT INTO student(sno,sname,sage,ssex) VALUES(5,'王弼','1982-6-21','男');
INSERT INTO student(sno,sname,sage,ssex) VALUES(6,'王丽','1984-10-10','女');
INSERT INTO student(sno,sname,sage,ssex) VALUES(7,'刘香','1980-12-22','女');
-- 课程表
CREATE TABLE course(
cno int NOT NULL PRIMARY KEY,
cname nvarchar(20) NOT NULL,
tno int NOT NULL
);
-- 添加外键
ALTER TABLE course
ADD CONSTRAINT fk_course_teacher
FOREIGN KEY (tno) REFERENCES teacher (tno);
insert into course(cno,cname,tno) values(1,'企业管理',3);
insert into course(cno,cname,tno) values(2,'马克思',1);
insert into course(cno,cname,tno) values(3,'UML',2);
insert into course(cno,cname,tno) values(4,'数据库',5);
insert into course(cno,cname,tno) values(5,'物理',8);
-- 创建成绩表
CREATE TABLE sc(
sno int NOT NULL,
cno int NOT NULL,
score int NOT NULL
);
ALTER TABLE sc
ADD CONSTRAINT fk_sc_course
FOREIGN KEY (cno) REFERENCES course (cno);
ALTER TABLE sc
ADD CONSTRAINT fk_sc_student
FOREIGN KEY (sno) REFERENCES student (sno);
INSERT INTO sc(sno,cno,score)VALUES(1,1,80);
INSERT INTO sc(sno,cno,score)VALUES(1,2,86);
INSERT INTO sc(sno,cno,score)VALUES(1,3,83);
INSERT INTO sc(sno,cno,score)VALUES(1,4,89);
INSERT INTO sc(sno,cno,score)VALUES(2,1,50);
INSERT INTO sc(sno,cno,score)VALUES(2,2,36);
INSERT INTO sc(sno,cno,score)VALUES(2,3,43);
INSERT INTO sc(sno,cno,score)VALUES(2,4,59);
INSERT INTO sc(sno,cno,score)VALUES(3,1,50);
INSERT INTO sc(sno,cno,score)VALUES(3,2,96);
INSERT INTO sc(sno,cno,score)VALUES(3,3,73);
INSERT INTO sc(sno,cno,score)VALUES(3,4,69);
INSERT INTO sc(sno,cno,score)VALUES(4,1,90);
INSERT INTO sc(sno,cno,score)VALUES(4,2,36);
INSERT INTO sc(sno,cno,score)VALUES(4,3,88);
INSERT INTO sc(sno,cno,score)VALUES(4,4,99);
INSERT INTO sc(sno,cno,score)VALUES(5,1,90);
INSERT INTO sc(sno,cno,score)VALUES(5,2,96);
INSERT INTO sc(sno,cno,score)VALUES(5,3,98);
INSERT INTO sc(sno,cno,score)VALUES(5,4,99);
INSERT INTO sc(sno,cno,score)VALUES(6,1,70);
INSERT INTO sc(sno,cno,score)VALUES(6,2,66);
INSERT INTO sc(sno,cno,score)VALUES(6,3,58);
INSERT INTO sc(sno,cno,score)VALUES(6,4,79);
INSERT INTO sc(sno,cno,score)VALUES(7,1,80);
INSERT INTO sc(sno,cno,score)VALUES(7,2,76);
INSERT INTO sc(sno,cno,score)VALUES(7,3,68);
INSERT INTO sc(sno,cno,score)VALUES(7,4,59);
INSERT INTO sc(sno,cno,score)VALUES(7,5,89);
-- 1、查询课程1的成绩比课程2的成绩高的所有学生的学号；
select a.sno from (select sno,score from sc where cno=1) a join (select sno,score from sc where cno=2) b on a.sno = b.sno where a.score > b.score;
-- 2、查询平均成绩大于60分的同学的学号和平均成绩；
select sno,avg(score) from sc group by sno having avg(score)>60;
-- 3、查询学过“叶平”老师所教所有课程的所有同学的学号、姓名；
select sno from (select sno,count(cno) num from sc where cno in (select cno from course where tno in (select tno from teacher where tname = '叶平'))group by sno) t where t.num = (select count(cno)from course where tno = (select tno from teacher where tname = '叶平'));
-- 4、查询所有课程成绩小于60分的同学的学号、姓名；
select sno,sname from student where sno in(select distinct sno from sc where score<60);
-- 5、查询所有同学的学号、姓名、选课数、总成绩；
select stu.sno,stu.sname,count(cno),sum(score) from student stu join sc s on stu.sno = s.sno group by stu.sno;
