How can the EXPLAIN command be used to assess the feasibility of creating a new index in a database?

The EXPLAIN command in SQL is used to analyze the execution plan of a query by the database. To assess whether creating a new index is justified, you can run EXPLAIN on the query you plan to optimize and see how the database executes it.

If EXPLAIN shows that the query performs a full table scan, and there is a field in the WHERE clause that could be indexed, creating an index can significantly speed up the query.

Example of usage:

EXPLAIN SELECT * FROM users WHERE email = 'example@example.com';

If the output indicates a full scan, you can create an index:

CREATE INDEX idx_users_email ON users(email);

After creating the index, run EXPLAIN again and compare the plans. If an index scan is now used, the index is effective.

Thus, EXPLAIN helps understand how much the query benefits from an index and whether it is worth creating one.