CODE EXAMPLE FOR SQL

create foreign key postgres

DROP TABLE IF EXISTS contacts;
DROP TABLE IF EXISTS customers;

CREATE TABLE customers(
   customer_id INT GENERATED ALWAYS AS IDENTITY,
   customer_name VARCHAR(255) NOT NULL,
   PRIMARY KEY(customer_id)
);

CREATE TABLE contacts(
   contact_id INT GENERATED ALWAYS AS IDENTITY,
   customer_id INT,
   contact_name VARCHAR(255) NOT NULL,
   phone VARCHAR(15),
   email VARCHAR(100),
   PRIMARY KEY(contact_id),
   CONSTRAINT fk_customer
      FOREIGN KEY(customer_id) 
	  REFERENCES customers(customer_id)
	  ON DELETE CASCADE
);

INSERT INTO customers(customer_name)
VALUES('BlueBird Inc'),
      ('Dolphin LLC');	   
	   
INSERT INTO contacts(customer_id, contact_name, phone, email)
VALUES(1,'John Doe','(408)-111-1234','john.doe@bluebird.dev'),
      (1,'Jane Doe','(408)-111-1235','jane.doe@bluebird.dev'),
      (2,'David Wright','(408)-222-1234','david.wright@dolphin.dev');
Code language: SQL (Structured Query Language) (sql)