alter table student disable constraint fk_student; --oracle

ALTER TABLE student ALTER FOREIGN KEY fk_student NOT ENFORCED; --DB2

ALTER TABLE student ADD CONSTRAINT FOREIGN KEY (college_id) REFERENCES college CONSTRAINT student_fk1; --增加外键

ALTER TABLE student DROP CONSTRAINT fk_student;--删除外键

alter table student add constraint fk_student foreign key(college_id) references college(college_id);

alter table student2 add constraint fk_student foreign key(college_id) references college(college_id);--oracle alter table student2 add constraint fk_student foreign key(college_id) references college(college_id);--db2 ALTER TABLE student ADD CONSTRAINT FOREIGN KEY (college_id) REFERENCES college CONSTRAINT student_fk1; --informix

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