Question

I have 2 tables:

id box_name hidden

---------------------------

id item_name box_id hidden

so the foreign key is box_id, if the box is deleted or updated it touches also the child items, but how can I make the same with the hidden fields, they are indexes with the same type int(11), if I hide some box, all the children are hidden, but how to hide only the children who references to the box_id -> id, those hidden???

or in other words, how to make 2 foreign keys

Answer 1

You can easily do this by adding unique constraint on parent table id,hidden fields and changing your detail table so it has FK to (id,hidden) rather than to just id. However, in this case I don’t see why you need to store hidden attribute in detail table since it’s always the same as parent hidden.

I’d rather add an after update trigger on master table that updates all necessary rows in detail table[s].

Update. Example.
1st approach

CREATE TABLE boxTable(id int not null auto_increment primary key,hidden 
tinyint not null,
...
CONSTRAINT UQ_BOXTABLE(id,hidden));
CREATE TABLE childTable(...., boxId int not null, hidden tinyint not null,
 CONSTRAINT FK_childTable_BoxTable FOREIGN KEY (boxId, hidden) REFERENCES 
 boxTable(boxId, hidden) ON DELETE CASCADE ON UPDATE CASCADE) ;

every time you change hidden in boxTable it will be automatically updated in childTable.

2nd approach (double check syntax, I don’t have mysql at the moment)

CREATE TRIGGER AU_boxTable AFTER UPDATE ON boxTable 
FOR EACH ROW
BEGIN 
  IF (new.hidden <> old.hidden) THEN 
    update childTable set hidden = new.hidden WHERE boxId = new.id;
  END IF;
END;

2nd approach allows you changing hidden fields in childTable regardless of value in boxTable, the first doesn’t.