Alter Tables

1. You have a table customers with a column email that currently allows NULL values. Modify the table so that future entries must always have an email. The email column in the customers table currently allows NULL values. To ensure every new record has an email, we modify the column and set it to NOT NULL. This prevents future entries from leaving it empty. 2. In the users table, ensure that the username column is unique across all records using an ALTER statement. To avoid duplicate usernames, we update the users table by adding a UNIQUE constraint on the username column. This guarantees that each username is distinct across all records. 3. In the products table, enforce that price must always be greater than 0 using an ALTER command. We modify the products table by adding a CHECK constraint on the price column. This ensures that every product must have a price greater than 0. 4. Modify the orders table so that the status column defaults to 'pending' if no value is provided during ins