Foreign key Method 1 - while creating table create table if not exists `student` ( key `fk_gradeId` ( `gradeId` ) , -- define key constraint `fk_gradeId` foreign key ( `gradeId` ) references `grade` ( `gradeId` ) -- add constranit + reference ) Method 2 - after create table alter table `students` add constraint `fk_gradeId` foreign key ( `gradeId` ) references `grade` ( `gradeId` ) The above two methods are physical foreign keys, database-level foreign keys, which are not recommended Best practice Database is only used to store data Using foreign keys by programming
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