CREATE TABLE TEACHER ( T# INT NOT NULL,
TNAME VARCHAR NOT NULL,
PRIMARY KEY(T#));
CREATE TABLE COURSE (C# INT NOT NULL,
T# VARCHAR NOT NULL,
CNAME VARCHAR NOT NULL,
RIMARY KEY (C#),
1 FOREIGN KEY T# REFERENCES T(T#));
2 CONSTRAINT FK FOREIGN KEY T# REFERENCES TEACHER(T#));
1和2是一个东西吗


效果一样，性质大不相同。特别在删除的时候
1，drop foreign key很尴尬，暂时不知道怎么写
2，alter table xx drop constraint fk