Creating Tables using constraints

In this assignment, I practiced creating tables with different constraints like PRIMARY KEY, NOT NULL, UNIQUE, CHECK, DEFAULT and FOREIGN KEY. 1.Students Table (Unique ID) CREATE TABLE students ( id SERIAL PRIMARY KEY , name TEXT , age INT ); 2.Employees Table (NOT NULL fields) CREATE TABLE employees ( id SERIAL PRIMARY KEY , name TEXT NOT NULL , email TEXT NOT NULL , phone_number TEXT ); 3.Users Table (Unique username & email) CREATE TABLE users ( id SERIAL PRIMARY KEY , username TEXT UNIQUE , email TEXT UNIQUE ); 4.Products Table (CHECK constraints) CREATE TABLE products ( id SERIAL PRIMARY KEY , name TEXT , price NUMERIC CHECK ( price > 0 ), stock INT CHECK ( stock >= 0 ) ); 5.Orders Table (DEFAULT values) CREATE TABLE orders ( id SERIAL PRIMARY KEY , status TEXT DEFAULT 'pending' , created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP ); 6.Accounts Table (UNIQUE + CHECK) CREATE TABLE accounts ( id SERIAL PRIMARY KEY , account_number TEXT UNIQUE NOT NULL , balance INT CHECK ( balance >= 0