sql add foreign key to existing column alter existing code example

Example 1: add new column in sql with foreign key

ALTER TABLE `fb_banners`
ADD `city_id` BIGINT(20) UNSIGNED NULL DEFAULT NULL AFTER `BannerID`,
ADD INDEX `Foreign_city_id_banners` (`city_id`) USING BTREE,
ADD CONSTRAINT `Foreign_city_id_banners` FOREIGN KEY (`city_id`) REFERENCES `foodsafari`.`fb_cities` (`id`) ON UPDATE CASCADE ON DELETE CASCADE;

Example 2: alter table add key sql server

ALTER TABLE Persons
ADD CONSTRAINT PK_Person PRIMARY KEY (ID,LastName);