为引用 SQL Plus 中不同表的多个主键的外键添加约束？

Question

我是一名学习 SQL 的初学者，在实施这个概念时遇到了困难。

假设你创建了以下三个表：

CREATE TABLE dogOwner(
 ownerNo VARCHAR(8) CONSTRAINT ownerNo_pk1 PRIMARY KEY,
 ownerName VARCHAR(10)
);

CREATE TABLE catOwner(
 ownerNo VARCHAR(8) CONSTRAINT ownerNo_pk2 PRIMARY KEY,
 ownerName VARCHAR(10)
);

CREATE TABLE petsAdopted(
 petNo VARCHAR(8) CONSTRAINT petNo_pk PRIMARY KEY,
 ownerNo VARCHAR(8) CONSTRAINT ownerNo_fk1 REFERENCES dogOwner(ownerNo)
                    CONSTRAINT ownerNo_fk2 REFERENCES catOwner(ownerNo)
);

您如何正确地为外键 ownerNo 创建约束，该外键从其他两个表中引用 ownerNo？

Answer 1

你不能。您可以在 petsAdopted 中有 2 列：dogOwnerNo 和 catOwnerNo 以及 2 个外键。但是桌子的设计似乎没有意义：不管谁拥有它，宠物肯定要么是狗要么是猫（或其他东西）？

这是另一种设计：

CREATE TABLE owner(
 ownerNo VARCHAR(8) CONSTRAINT ownerNo_pk2 PRIMARY KEY,
 ownerName VARCHAR(10)
);

CREATE TABLE petsAdopted(
 petNo VARCHAR(8) CONSTRAINT petNo_pk PRIMARY KEY,
 petType VARCHAR2(10) NOT NULL CONSTRAINT petTypeChk (CHECK petType in ('CAT','DOG'))
 ownerNo VARCHAR(8) CONSTRAINT ownerNo_fk REFERENCES owner(ownerNo)
);

Answer 2

这仅解决您答案的语法部分，您有很多语法错误，但这不起作用，请重新考虑您的设计。

 CREATE TABLE dogOwner(
 ownerNo VARCHAR(8) CONSTRAINT ownerNo_pk1 PRIMARY KEY,
 ownerName VARCHAR(10)
);

CREATE TABLE catOwner(
 ownerNo VARCHAR(8),
 ownerName VARCHAR(10),
 CONSTRAINT ownerNo_pk2 PRIMARY KEY (ownerNo),
 CONSTRAINT ownerNo_fk1  FOREIGN KEY (ownerNo) REFERENCES dogOwner(ownerNo)
);

CREATE TABLE petsAdopted(
 petNo VARCHAR(8) ,
 ownerNo VARCHAR(8),
CONSTRAINT petNo_pk PRIMARY KEY (petNo),
CONSTRAINT ownerNo_fk_pet1 FOREIGN KEY (ownerNo) REFERENCES dogOwner(ownerNo),
CONSTRAINT ownerNo_fk_pet2  FOREIGN KEY (ownerNo) REFERENCES catOwner(ownerNo)
);