Data importing

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C#

SQL

I am working on a project in which I am importing data from several foreign data sources (i.e. sybase, foxpro, etc.). Rather than processing each record as if it has been updated, I am looking for some advice on how to determine if the record has changed prior to collecting all of the data from the source and going through all of the processing steps that are required... Some of the tables have upwards of a million rows and each row requires a lookup in the production table. I had originally thought of using a hash value... collecting all of the data from the source then computing a hash value, and comparing the hash in the production table to the one generated. If different, then update, else move on. From the research i did, it does not appear that the hash will be the same each time it gets generated.. Any help would be great!

Thanks!

Craig