Walter, the use of a second table (the Extended Customer Info, for example) is great when you have a little bit of information on ALL of your customers, and a LOT of information on only a FEW of your customers and you don't want to waste space in your primary table.

For example, let's say you have name, address, and phone number on ALL or most of your customers, but you only have buying habits and demographic data on about 10% of them. This is where an extended table and a one-to-one relationship comes in perfect.