fix mistakes

dmedvedev/ddl.sql

@@ -1,4 +1,5 @@
-CREATE TABLE users (
+CREATE TABLE users
+(
   id INT PRIMARY KEY NOT NULL,
   name VARCHAR(100) NOT NULL,
   age INT,
@@ -8,7 +9,8 @@ CREATE TABLE users (
   created_at TIMESTAMPTZ NOT NULL
 );
 
-CREATE TABLE products (
+CREATE TABLE products
+(
   id INT PRIMARY KEY NOT NULL,
   name VARCHAR(100) NOT NULL,
   category VARCHAR(50),
@@ -16,15 +18,17 @@ CREATE TABLE products (
   in_stock BOOLEAN
 );
 
-CREATE TABLE orders (
-  id INT PRIMARY KEY NOT NULL,
+CREATE TABLE orders
+(
+  id SERIAL PRIMARY KEY NOT NULL,
   user_id INT,
   order_date TIMESTAMPTZ NOT NULL,
   status VARCHAR(20),
   FOREIGN KEY (user_id) REFERENCES users(id)
 );
 
-CREATE TABLE order_items (
+CREATE TABLE order_items
+(
   order_id INT NOT NULL,
   product_id INT NOT NULL,
   quantity INT NOT NULL,