This article has been long overdue; so I apologize to newbie who orignally asked how to do duplicate key checking before inserting Excel data into a MySQL database.
I got a few minutes of free time today, so I decided to draft a sample workbook that will demonstrate this process. You can download the sample workbook here. Standard disclaimer: This file has been found to be virus-free when uploaded. However, you are highly recommended to scan the file again with an up to date anti-virus software before opening it.