fix postgres

dsolovianov/postgresql/DDL.sql

@@ -1,5 +1,5 @@
 CREATE TABLE dsolovianov.users (
-    id			INT GENERATED ALWAYS AS IDENTITY NOT NULL,
+    id			INT GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
     name		VARCHAR(100) NOT NULL,
     age			INT,
     email		VARCHAR(100),
@@ -9,7 +9,7 @@ CREATE TABLE dsolovianov.users (
 );
 
 CREATE TABLE dsolovianov.products (
-	id			INT GENERATED ALWAYS AS IDENTITY NOT NULL,
+	id			INT GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
 	name		VARCHAR(100) NOT NULL,
 	category	VARCHAR(50),
 	price		DECIMAL(10,2) NOT NULL,
@@ -17,7 +17,7 @@ CREATE TABLE dsolovianov.products (
 	);
 
 CREATE TABLE dsolovianov.orders (
-    id			INT GENERATED ALWAYS AS IDENTITY NOT NULL,
+    id			INT GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
     user_id		INT,
     order_date  TIMESTAMPTZ NOT NULL,
     status		VARCHAR(20)
@@ -26,7 +26,11 @@ CREATE TABLE dsolovianov.orders (
 CREATE TABLE dsolovianov.order_items (
     order_id           INT NOT NULL,
     product_id         INT NOT NULL,
-    quantity           INT NOT NULL,
-    price_at_purchase  DECIMAL(10,2) NOT NULL,
+    quantity           INT NOT NULL CHECK (quantity > 0),
+    price_at_purchase  DECIMAL(10,2) NOT NULL CHECK (price_at_purchase > 0),
     CONSTRAINT order_items_pk PRIMARY KEY (order_id, product_id)
+    CONSTRAINT order_items_order_fk
+    	FOREIGN KEY (order_id) REFERENCES dsolovianov.orders(id),
+    CONSTRAINT order_items_product_fk
+    	FOREIGN KEY (product_id) REFERENCES dsolovianov.products(id)
 );