Question

Basically, I want to get all rows from the customers table that do NOT appear in the brochure_requests table.

SELECT *      
  FROM customers  JOIN  brochure_requests
    WHERE brochure_requests.first_name != customers.customer_first_name
    AND brochure_requests.last_name != customers.customer_last_name

The query works when the parameters are =, but as soon as I run a != query, the program (HeidiSQL) hangs indefinitely or until I cancel it.

Answer 1

Use NOT EXISTS, e.g.

SELECT *      
FROM customers 
WHERE NOT EXISTS (
    SELECT 1
    FROM   brochure_requests
    WHERE  brochure_requests.first_name = customers.customer_first_name
    AND    brochure_requests.last_name = customers.customer_last_name)

I would also suggest adding an index on the brochure_requests.first_name and brochure_requests.last_name fields for improved performance.