made changes PRIMARY KEY and FOREIGN KEY

dmedvedev/ddl.sql

@@ -20,7 +20,8 @@ CREATE TABLE orders (
   id INT PRIMARY KEY NOT NULL,
   user_id INT,
   order_date TIMESTAMPTZ NOT NULL,
-  status VARCHAR(20) 
+  status VARCHAR(20),
+  FOREIGN KEY (user_id) REFERENCES users(id)
 );
 
 CREATE TABLE order_items (
@@ -28,5 +29,7 @@ CREATE TABLE order_items (
   product_id INT NOT NULL,
   quantity INT NOT NULL,
   price_at_purchase DECIMAL(10,2) NOT NULL,
-  PRIMARY_KEY (order_id, product_id)
+  PRIMARY KEY (order_id, product_id),
+  FOREIGN KEY (order_id) REFERENCES orders(id),
+  FOREIGN KEY (product_id) REFERENCES products(id)
 );