mysql外键使用主键

Question

I have two tables, diary with columns id primary key Narrative text and master with columns id primary key Diaryid int EventDate date Location int

I want to ensure that master(Diaryid) is always a valid diary(id)

Can I use foreign key to achieve this? Bearing in mind that one key is a primary key and the other int.

Any advice would be apprecaited.

Answer 1

Yes you cqan achieve this by using a FOREIGN KEY .

Also you should define it as NOT NULL, so that only exiasting diary keys are allowed

CREATE TABLE master(Diaryid BIGINT NOT NULL
,  FOREIGN KEY (Diaryid)
        REFERENCES diary(id)
        );

You cqan add

ON DELETE CASCADE

So that the Master row will be deleted also when the diary rows gets removed

Answer 2

Don't know what is different but problem is solved. CREATE TABLE diary (id int AUTO_INCREMENT, Narrative text, PRIMARY KEY( id )) CREATE TABLE master ( id int AUTO_INCREMENT, Diaryid int, datemade date, FOREIGN KEY( Diaryid ) REFERENCES diary ( id ), primary key (id)) So am now adding diary records and can have multiple master records so long as the Diaryid is valid Thanks