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| //步骤1:画E-R图
//步骤2:分别建实体表,并给多方的表添加外键约束
CREATE TABLE person2(
id VARCHAR(32) PRIMARY KEY,
pname VARCHAR(30),
sex CHAR(1)
);
CREATE TABLE car(
id VARCHAR(32) PRIMARY KEY,
cname VARCHAR(30),
price NUMERIC(10,2),
pid VARCHAR(32),
CONSTRAINT car_fk FOREIGN KEY(pid) REFERENCES person2(id)
);
DROP TABLE car;
//步骤3:为两个表添加测试数据
//实体表1
INSERT INTO person2(id,pname,sex) VALUES('P001','Jack','1');
INSERT INTO person2(id,pname,sex) VALUES('P002','Tom','1');
INSERT INTO person2(id,pname,sex) VALUES('P003','Rose','0');
INSERT INTO person2(id,pname,sex) VALUES('P004','Mary','0');
INSERT INTO person2(id,pname,sex) VALUES('P005','Mike','1');
SELECT * FROM person2;
////实体表2
INSERT INTO car(id,cname,price,pid) VALUES('C001','BMW',123.5,'P001');
INSERT INTO car(id,cname,price,pid) VALUES('C002','Benz',123.5,'P001');
INSERT INTO car(id,cname,price,pid) VALUES('C003','BMW',223.5,'P001');
INSERT INTO car(id,cname,price,pid) VALUES('C011','BMW',83.5,'P003');
INSERT INTO car(id,cname,price,pid) VALUES('C012','Benz',100,'P003');
INSERT INTO car(id,cname,price,pid) VALUES('C013','Audi',223.5,'P003');
INSERT INTO car(id,cname,price,pid) VALUES('C021','BMW',88.5,'P004');
INSERT INTO car(id,cname,price,pid) VALUES('C022','QQ',10,'P004');
INSERT INTO car(id,cname,price,pid) VALUES('C023','Audi',73,'P005');
INSERT INTO car(id,cname,price) VALUES('C033','Audi',1000);
//该句代码执行错误,因为编号为P006的人在Person2表中不存在,这就是参照完整性
INSERT INTO car(id,cname,price,pid) VALUES('C033','Audi',1000,'P006');
SELECT * FROM car;
//查询:哪些人有什么样的车 (用"表名.列名"的形式访问列,如果列名不重复,可以省略表名)
//利用一方的主键和“多方”的外键进行关联
SELECT person2.pname,car.cname FROM person2,car WHERE person2.id=car.pid;
//查询Jack有什么车
SELECT person2.pname,car.cname FROM person2,car WHERE person2.id=car.pid AND person2.pname='Jack' ;
//查询哪些人有两辆以上的车
SELECT person2.pname,COUNT(pname) AS 车数量 FROM person2,car WHERE person2.id=car.pid GROUP BY pname HAVING COUNT(pname)>=2 ORDER BY 车
数量;
SELECT * FROM person2 WHERE id IN ( SELECT pid FROM car GROUP BY pid HAVING COUNT(pid)>=2 );
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