CA 40 – Alter Tables

This exercise was about ALTER TABLE. Instead of creating table again, we modify existing table like adding constraints, defaults, columns etc. Make email NOT NULL in customers table sql id="h4r9b2" ALTER TABLE customers ALTER COLUMN email SET NOT NULL; This makes sure future rows must have email. Make username unique in users table sql id="9zv1qx" ALTER TABLE users ADD CONSTRAINT unique_username UNIQUE (username); This prevents duplicate usernames. Add check constraint price > 0 in products table sql id="g6p8la" ALTER TABLE products ADD CONSTRAINT price_check CHECK (price > 0); Now price cannot be zero or negative. Set default status 'pending' in orders table sql id="s8k3po" ALTER TABLE orders ALTER COLUMN status SET DEFAULT 'pending'; If status not given, it will automatically become pending. Add salary column in employees table with conditions sql id="x2w7mn" ALTER TABLE employees ADD COLUMN salary INT NOT NULL; ALTER TABLE employees ADD CONSTRAINT salary_check CHECK (salary > 10000)