Alter Queries

In this assignment, I worked on modifying existing tables using ALTER TABLE. This helped me understand how to update constraints without recreating tables. 1.Make email NOT NULL in customers ALTER TABLE customers ALTER COLUMN email SET NOT NULL; 2.Make username UNIQUE in users ALTER TABLE users ADD CONSTRAINT unique_username UNIQUE (username); 3.Add CHECK constraint on price > 0 in products ALTER TABLE products ADD CONSTRAINT price_check CHECK (price > 0); 4.Set default 'pending' for status in orders ALTER TABLE orders ALTER COLUMN status SET DEFAULT 'pending'; 5.Add salary column with constraints in employees ALTER TABLE employees ADD COLUMN salary INT NOT NULL CHECK (salary > 10000); 6.Modify foreign key with CASCADE ALTER TABLE employees DROP CONSTRAINT employees_department_id_fkey; ALTER TABLE employees ADD CONSTRAINT employees_department_id_fkey FOREIGN KEY (department_id) REFERENCES departments(id) ON DELETE CASCADE; 7.Remove CHECK constraint on balance in accounts ALTER