數據庫練習

請建立以下表：並建立相關約束

CREATE table class(
cid int PRIMARY key,
caption varchar(10)
);
INSERT INTO class VALUES(1,'三年二班');
INSERT INTO class VALUES(2,'一年三班');
INSERT INTO class VALUES(3,'三年一班');

create table student(
sid int PRIMARY key,
sname varchar(10),
gender varchar(10),
class_id int,
FOREIGN KEY(class_id) REFERENCES class(cid)
);
insert into student VALUES(1,'張三','女',1);
insert into student VALUES(2,'李四','女',1);
insert into student VALUES(3,'王五','男',2);

create table teacher(
tid int primary key,
tname varchar(10)
);

insert into teacher VALUES(1,'馬雲');
insert into teacher VALUES(2,'馬化騰');
insert into teacher VALUES(3,'俞敏洪');

CREATE table course(
cid int primary KEY,
cname varchar(10),
teacher_id int ,
FOREIGN KEY(teacher_id) REFERENCES teacher(tid)
);

insert into course VALUES(1,'生物',1);
insert into course VALUES(2,'體育',1);
insert into course VALUES(3,'物理',2);

create table score(
sid int PRIMARY key,
student_id int,
FOREIGN key(student_id) REFERENCES student(sid),
course_id int,
FOREIGN key(course_id) references course(cid),
number int
);
insert into score VALUES(1,1,1,58);
insert into score VALUES(2,1,2,68);
insert into score VALUES(3,2,2,89);

 

操做表：

1.查詢平均成績大於60分的同窗的學號和平均成績；

SELECT
t1.sid 學生編號,
AVG( t2.number ) 平均分
FROM
student t1
LEFT JOIN score t2 ON t1.sid = t2.student_id
GROUP BY
t1.sid
HAVING
AVG( t2.number ) > 60

 

2.查詢全部同窗的學號、姓名、選課數、總成績；

SELECT
t1.sid "編號",
t1.sname "姓名",
t2.temp1 "選課數",
t2.temp2 "總分"
FROM
student t1,
( SELECT student_id, COUNT( sid ) temp1, SUM( number ) temp2 FROM score GROUP BY student_id ) t2
WHERE
t1.sid = t2.student_id;

 

3..查詢姓「馬」的老師的個數；

SELECT
COUNT( tid )
FROM
teacher
WHERE
tname LIKE "馬%"

4.查詢有課程成績小於60分的同窗的學號、姓名；

SELECT DISTINCT
t1.sid "學號",
t1.sname "姓名"
FROM
student t1
LEFT JOIN score t2 ON t2.student_id = t1.sid
WHERE
t2.number < 60;

5查詢至少有一門課與學號爲「001」的同窗所學相同的同窗的學號和姓名；

SELECT DISTINCT t1.student_id, t2.sname FROM score t1 LEFT JOIN student t2 ON t1.student_id = t2.sid WHERE course_id IN ( SELECT course_id FROM score WHERE student_id = 2 )；