Write a query to display all the customers whose ID is 2001 below the salesperson ID of Mc Lyon.

Sure, here is a SQL query that would display all the customers whose ID is 2001 and are under the salesperson ID of Mc Lyon.

Please note that the exact query might vary depending on the structure of your database. I'm assuming you have a table named 'customers' with fields 'customer_id' and 'salesperson_id', and a table named 'salespersons' with fields 'salesperson_id' and 'salesperson_name'.

SELECT * 
FROM customers 
WHERE customer_id = 2001 
AND salesperson_id IN (
    SELECT salesperson_id 
    FROM salespersons 
    WHERE salesperson_name = 'Mc Lyon'
);

This query works in the following way:

1. The subquery (the part in brackets) selects the ID of the salesperson named 'Mc Lyon' from the 'salespersons' table.
2. The main query then selects all records from the 'customers' table where the 'customer_id' is 2001 and the 'salesperson_id' is the same as the one we found in the subquery.