Question

I have these database

  === Invoices ===
   id
   status
   description

   === Invoice Items ===
   id
   invoice_id (FK)
   item_name
   description

To make this table I have made this MySQL command

CREATE TABLE IF NOT EXISTS `nt_invoices` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `status` varchar(45) NOT NULL DEFAULT '',
  `description` text NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM  DEFAULT CHARSET=latin1 AUTO_INCREMENT=24 ;


CREATE TABLE IF NOT EXISTS `nt_invoice_items` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `invoice_id` int(11) NOT NULL,
  `item_name` varchar(45) NOT NULL,
  `description` text NOT NULL,
  PRIMARY KEY (`id`),
  KEY `invoice_id` (`invoice_id`)
) ENGINE=MyISAM  DEFAULT CHARSET=latin1 AUTO_INCREMENT=12 ;

My problem is that I want to declare a foreign key in the invoice_items table and to make the invoice_id the foreign key of invoices table id. So how to write that command? Any help and suggestions will be highly appreciated.

Answer 1

You should have innodb engine type for using foreign keys.

CREATE TABLE IF NOT EXISTS `nt_invoice_items` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `invoice_id` int(11) NOT NULL references nt_invoices(id)
  `item_name` varchar(45) NOT NULL,
  `description` text NOT NULL,
  PRIMARY KEY (`id`),
  KEY `invoice_id` (`invoice_id`)
) ENGINE=INNODB DEFAULT CHARSET=utf8;

OR if you want to use cascaded update delete:

CREATE TABLE IF NOT EXISTS `nt_invoice_items` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `invoice_id` int(11) NOT NULL,
  `item_name` varchar(45) NOT NULL,
  `description` text NOT NULL,
  PRIMARY KEY (`id`),
  KEY `invoice_id` (`invoice_id`),
 FOREIGN KEY (invoice_id) REFERENCES  nt_invoices(id)
   ON DELETE CASCADE
   ON UPDATE CASCADE,

) ENGINE=INNODB DEFAULT CHARSET=utf8;