Visual FoxPro Table Comparison

I’m using Visual FoxPro 6.0 and I’m trying to create a query that would select records out of one table that are not in a second table and since I have very large tables I need it to be quick. I’ve been able to get the desired result but it’s slow. I’ve not been able to find a true “comparison” for tables. Does anyone have any suggestions? Thanks, JMartin