mysql foreign key error #1452

Question

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

`id`
) ON DELETE CASCADE ;

MySQL said: 

#1452 - Cannot add or update         


        

Answer 1

Checks that "companies" table is not empty,if is empty and you have no data at moment.

 set SET FOREIGN_KEY_CHECKS = 0; 

like Ike said you before.