Hi Neil, Yes, primary key is always unique.
In your case, you are using composite key (players_id,default_teams_id). _Krishna On Wed, Oct 13, 2010 at 8:07 PM, Tompkins Neil <neil.tompk...@googlemail.com > wrote: > I've the following table. But why isn't the primary key unique, e.g. > preventing duplicates if entered ? > > CREATE TABLE `players_master` ( > > `players_id` bigint(20) NOT NULL AUTO_INCREMENT, > `default_teams_id` bigint(20) NOT NULL, > `first_name` varchar(100) COLLATE utf8_unicode_ci NOT NULL, > `second_name` varchar(100) COLLATE utf8_unicode_ci NOT NULL, > `known_as` varchar(200) COLLATE utf8_unicode_ci DEFAULT NULL, > `dob` date NOT NULL, > `countries_id` char(2) COLLATE utf8_unicode_ci NOT NULL, > `retirement_date` date DEFAULT NULL, > `positions_id` varchar(3) COLLATE utf8_unicode_ci NOT NULL, > `estimated_value` double NOT NULL DEFAULT '0', > `contract_wage` double NOT NULL DEFAULT '0', > `rating` int(11) NOT NULL, > PRIMARY KEY (`players_id`,`default_teams_id`), > KEY `FK_players_master_countries_id` (`countries_id`), > KEY `FK_players_master_positions_id` (`positions_id`), > KEY `IDX_first_name` (`first_name`), > KEY `IDX_known_as` (`known_as`), > KEY `IDX_second_name` (`second_name`), > KEY `IDX_dob` (`dob`), > KEY `IDX_estimated_value` (`estimated_value`), > KEY `IDX_contract_wage` (`contract_wage`), > KEY `IDX_rating` (`rating`), > KEY `FK_players_master_teams_id` (`default_teams_id`), > CONSTRAINT `FK_players_master_countries_id` FOREIGN KEY (`countries_id`) > REFERENCES `countries` (`countries_id`) ON DELETE NO ACTION ON UPDATE NO > ACTION, > CONSTRAINT `FK_players_master_positions_id` FOREIGN KEY (`positions_id`) > REFERENCES `positions` (`positions_id`) ON DELETE NO ACTION ON UPDATE NO > ACTION, > CONSTRAINT `FK_players_master_teams_id` FOREIGN KEY (`default_teams_id`) > REFERENCES `teams_master` (`teams_id`) ON DELETE NO ACTION ON UPDATE NO > ACTION > ) ENGINE=InnoDB AUTO_INCREMENT=1001 DEFAULT CHARSET=utf8 > COLLATE=utf8_unicode_ci > > I'm confused, I thought primary keys were always unique ? > > Cheers > Neil >
