What causes 'access denied for user' in sql?

Example:

While trying to connect to the database:

Access denied for user 'john'@'localhost' (using password: YES)

You're facing a permission issue while trying to access the database.

Solution:

Ensure that the username and password are correct, and that the user has the appropriate permissions to access the database. Consult with the database administrator if necessary.

-- Not an SQL solution, but you might need to check user permissions or reset the password.