mysql mariadb foreign key code example

Example 1: mariadb add foreign key

alter table group_a 
add constraint fk_b_in_a
foreign key(`b_id`) 
    references group_b(`b_id`)
    on delete set null
    on update set null;

Example 2: create table in mysql mariadb primary key foreign key

CREATE TABLE IF NOT EXISTS `scores` (
  `ID` int(11) NOT NULL AUTO_INCREMENT,
  UserId int(11) NOT NULL,
  `NICKNAME` varchar(50) NOT NULL,
  `HIGHSCORE` int(11) NOT NULL,
  PRIMARY KEY (`ID`),
  FOREIGN KEY (UserId) REFERENCES USER(Id)
);