I have a csv file that has a list of books that I offer on my website. There are quantity, date available, and weight columns in this file that I would like updated using a file provided by my book distributor. The data file provided by my distributor is a fixed width .dat file that is around 500-600mb (I can provide position and width of the colum data). This file has over 2million books. I only need information on the 7000 or so books I offer on my site. The common field on both files is the UPC or ISBN Code.
What I need is a fast, easy and efficient way to update this data. It can be done in any manner offline or online that you suggest, but has to result in a tab delimited file and I have to be able to update it myself weekly.