sql add column foreign key code example

Example 1: sql foreign key

# A foreign key is essentially a reference to a primary
# key in another table.

# A Simple table of Users, 
CREATE TABLE users(
	userId INT NOT NULL,
  	username VARCHAR(64) NOT NULL,
  	passwd VARCHAR(32) NOT NULL,
  	PRIMARY KEY(userId);
);
# Lets add a LEGIT user!
INSERT INTO users VALUES(1000,"Terry","Teabagface$2");

# We will create an order table that holds a reference
# to an order made by our Terry
CREATE TABLE orders(
	orderId INT NOT NULL,
  	orderDescription VARCHAR(255),
  	ordererId INT NOT NULL,
  	PRIMARY KEY(orderId),
  	FOREIGN KEY (ordererId) REFERENCES users(userId)
);
# Now we can add an order from Terry
INSERT INTO orders VALUES(0001,"Goat p0rn Weekly",1000);

# Want to know more about the plight of Goats?
# See the link below

Example 2: add constraint fk

ALTER TABLE Orders
ADD CONSTRAINT FK_PersonOrder
FOREIGN KEY (PersonID) REFERENCES Persons(PersonID);

Example 3: 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;