相关疑难解决方法(0)

ALTER TABLE  `groups` ADD FOREIGN KEY (  `company_id` ) REFERENCES  `summaries`.`companies` (

`id`
) ON DELETE CASCADE ;

MySQL said: 

#1452 - Cannot add or update a child row: a foreign key constraint fails (`summaries/#sql-164a_33c`, CONSTRAINT `#sql-164a_33c_ibfk_1` FOREIGN KEY (`company_id`) REFERENCES `companies` (`id`) ON DELETE CASCADE) 

companies.id 是 primary auto increment int(11)

company_id 是 index int(11)

我不明白错误信息.任何人都可以对此有所了解吗？