CREATE TABLE `wr3_user` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`username` varchar(45) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;CREATE TABLE `wr3_user_option` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`user_id` int(11) unsigned NOT NULL DEFAULT '0',
`name` varchar(45) NOT NULL,
`val` varchar(45) NOT NULL,
PRIMARY KEY (`id`),
KEY `user_id` (`user_id`),
CONSTRAINT `wr3_user_option_ibfk_1` FOREIGN KEY (`user_id`) REFERENCES `wr3_user` (`id`) ON DELETE CASCADE ON UPDATE NO ACTION
) ENGINE=InnoDB DEFAULT CHARSET=utf8;KEY `user_id` (`user_id`), или внешняя ссылка уже является ключем? 
MySQL requires indexes on foreign keys and referenced keys so that foreign key checks can be fast and not require a table scan. In the referencing table, there must be an index where the foreign key columns are listed as the first columns in the same order. Such an index is created on the referencing table automatically if it does not exist. This index might be silently dropped later, if you create another index that can be used to enforce the foreign key constraint. index_name, if given, is used as described previously.https://dev.mysql.com/doc/refman/5.7/en/create-tab...
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