Question

I’m having some trouble using constraints correctly.

I have three tables, ‘item’, ‘store’ and ‘link_item_store’.
An Item can be in one or many stores, and one or many stores can have an item.
Since this is a many to many relationship, I’m using ‘link_item_store’ to normalize.

If I delete an item, I have to remove all instancs of that item in the ‘link_item_store’ table. And the same goes for store. This is my table and it’s constraints:

CREATE TABLE `link_item_store` (
  `fk_storeID` int(11) unsigned NOT NULL,
  `fk_itemID` int(11) unsigned NOT NULL,
  PRIMARY KEY  (`fk_storeID`,`fk_itemID`),
  KEY `fk_storeID` (`fk_storeID`),
  KEY `fk_itemID` (`fk_itemID`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 COLLATE=latin1_danish_ci;

ALTER TABLE `link_item_store`
  ADD CONSTRAINT `link_item_store_ibfk_2` FOREIGN KEY (`fk_itemID`) REFERENCES `link_item_store (`fk_itemID`) ON DELETE CASCADE,
  ADD CONSTRAINT `link_item_store_ibfk_1` FOREIGN KEY (`fk_storeID`) REFERENCES `link_item_store` (`fk_storeID`) ON DELETE CASCADE;

And heres is an example list:

fk_storeID, fk_itemID, itemName, storeName
11  7277    item 1  Test store
11  7278    item 2  Test store
11  7280    item 3  Test store
12  7277    item 1  Test store 2
12  7278    item 2  Test store 2
12  7290    item 4  Test store 2
35  7295    item 4  Test store 4
35  7299    item 5  Test store 4
35  7300    item 6  Test store 4
35  7302    item 7  Test store 4

My problem is that if I delete ‘item 7’ from ‘item’ table, ALL references are deleted from link_item_store. 🙁

What to do?

Update:
By having these two constraints on the table, I’m not able to insert new data to the table. I get the following error message:

Unable to query local database <b>Cannot add or update a child row: a foreign 
key constraint fails ( `link_item_store`, CONSTRAINT 
`link_item_store_item_ibfk_1` FOREIGN KEY (`fk_storeID`) REFERENCES 
`link_item_store` (`fk_storeID`) ON DELETE CASCADE)</b><br> INSERT INTO 
link_item_store (fk_storeID, fk_itemID) VALUES ('11', '7295')

Update 2 – Solution:
Michael pointed out to me that the ADD CONSTRAINT didn’t look right. On a closer look, I saw that he was right. This is the code that is generated by PhpMuAdmin upon adding constraints:

ALTER TABLE `link_item_store` ADD FOREIGN KEY ( `fk_itemID` ) REFERENCES `mydatabase`.`link_item_store` (`fk_itemID`) ON DELETE CASCADE ;

As you can see, the foreign key is reffering to itself! This defenetily have to be a bug in PhPMyAdmin.

The solution was to change reference. This works and I no longer have problems adding new records to the table:

ALTER TABLE `link_item_store` ADD FOREIGN KEY ( `fk_itemID` ) REFERENCES `mydatabase`.`item` (`id`) ON DELETE CASCADE ;

Answer 1

The syntax of your foreign keys seems unusual to me.

Instead of:

ADD CONSTRAINT `link_item_store_ibfk_2` FOREIGN KEY (`fk_itemID`) REFERENCES `link_item_store` (`fk_itemID`) ON DELETE CASCADE

Try:

 ADD CONSTRAINT `link_item_store_ibfk_2` FOREIGN KEY (`fk_itemID`) REFERENCES item (`itemID`) ON DELETE CASCADE

(Assuming itemID is the name of the correct column on the item table)