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) ); 7