alter table 子表 add constraint 外键约束名 foreign key (子表外键字段) references 父表(父表主键字段)


--添加外键并且会添加该外键字段

ALTER TABLE customerformentries ADD CONSTRAINT FOREIGN operationroleid REFERENCES operationroles(ID) ;    

--仅仅只添加外键

ALTER TABLE customerformentries ADD CONSTRAINT fk_cfe_operationroleid FOREIGN KEY (operationroleid) REFERENCES operationroles(ID) ;on update cascade /on delete cascade

on update cascade是级联更新的意思，on delete cascade是级联删除的意思，意思就是说当你更新或删除主键表，那外见表也会跟随一起更新或删除

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