为salerecord表CID字段添加外键，引用client表中CID字段。
A: ALTER TABLE salerecord ADD CONSTRAINT fk1 FOREIGN KEY(CID) REFERENCES client(CID);
B: ALTER TABLE salerecord ADD CONSTRAINT pk1 PRIMARY KEY(CID) REFERENCES client(CID);
C: ALTER TABLE salerecord ADD CONSTRAINT fk1 FOREIGN KEY(CID) REFERENCES client(CID),ADD CONSTRAINT pk2 PRIMARY KEY(GID) REFERENCES goods(GID);
D: ALTER TABLE salerecord ADD CONSTRAINT pk1 PRIMARY KEY(CID) REFERENCES client(CID),ADD CONSTRAINT pk2 PRIMARY KEY(GID) REFERENCES goods(GID);
A: ALTER TABLE salerecord ADD CONSTRAINT fk1 FOREIGN KEY(CID) REFERENCES client(CID);
B: ALTER TABLE salerecord ADD CONSTRAINT pk1 PRIMARY KEY(CID) REFERENCES client(CID);
C: ALTER TABLE salerecord ADD CONSTRAINT fk1 FOREIGN KEY(CID) REFERENCES client(CID),ADD CONSTRAINT pk2 PRIMARY KEY(GID) REFERENCES goods(GID);
D: ALTER TABLE salerecord ADD CONSTRAINT pk1 PRIMARY KEY(CID) REFERENCES client(CID),ADD CONSTRAINT pk2 PRIMARY KEY(GID) REFERENCES goods(GID);
举一反三
- 为salerecord表GID字段添加外键，引用goods表中GID字段。 A: ALTER TABLE salerecord ADD CONSTRAINT pk2 PRIMARY KEY(GID) REFERENCES goods(GID); B: ALTER TABLE salerecord ADD CONSTRAINT fk2 FOREIGN KEY(GID) REFERENCES goods(GID); C: ALTER TABLE salerecord ADD CONSTRAINT fk2 FOREIGN KEY(CID) REFERENCES goods(CID); D: ALTER TABLE salerecord ADD CONSTRAINT pk2 PRIMARY KEY(CID) REFERENCES goods(CID);
- 如何在已经创建好的表上添加一个外键约束:。 A: alter table 表名 add constraint foreign key (键名) references 关联表（关联键名） B: alter table 表名 add primary key (键名) references 关联表（关联键名） C: alter table 表名 add foreign key (键名) references （关联键名） D: alter table 表名 add constraint primary key (键名) references 关联表（关联键名）
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