SQL: Adding a New Column to an Existing Table

You are tasked with enhancing an existing database by adding a new column to a table. This is a common operation in database management, allowing you to store new types of information without having to drop and recreate the entire table. You will demonstrate your understanding of the ALTER TABLE statement in SQL.

Problem Description

Your goal is to add a new column named email to an existing table called customers. The email column should be of type VARCHAR and have a maximum length of 255 characters. It's important to ensure that this operation can be performed without affecting the existing data in the customers table.

Key Requirements:

• Modify the customers table.
• Add a new column named email.
• The data type of the email column must be VARCHAR.
• The maximum length of the email column should be 255 characters.
• The operation should be idempotent if the column already exists (meaning running it multiple times should not cause an error, though for this challenge we will assume it doesn't exist beforehand).

Expected Behavior:

After successfully executing the SQL statement, the customers table schema will be updated to include the email column. Any subsequent queries that select from customers will now include this new column. For existing rows, this new column will initially contain NULL values unless a default value is specified (which is not required for this problem).

Examples

Example 1:

Input:
An existing `customers` table with columns `customer_id` (INT) and `name` (VARCHAR(100)).

Output:
A modified `customers` table schema that includes `customer_id` (INT), `name` (VARCHAR(100)), and `email` (VARCHAR(255)).

Explanation: The ALTER TABLE statement is used to add the email column with the specified data type and length to the customers table.

Example 2:

Input:
A `customers` table with columns `customer_id` (INT), `name` (VARCHAR(100)), and `address` (VARCHAR(255)).

Output:
A modified `customers` table schema that includes `customer_id` (INT), `name` (VARCHAR(100)), `address` (VARCHAR(255)), and `email` (VARCHAR(255)).

Explanation: The ALTER TABLE statement is applied to add the email column, demonstrating that it works correctly even when other columns already exist.

Constraints

• The customers table is guaranteed to exist in the database.
• The email column does not exist in the customers table prior to executing the solution.
• The SQL dialect used should be standard SQL, compatible with most relational database systems.

Notes

Consider the general syntax for modifying table structures in SQL. The ALTER TABLE statement is your primary tool here. You will need to specify the table to modify, the action to perform (adding a column), the name of the new column, and its data type with any necessary parameters (like length for VARCHAR).