Before closing this chapter, I'd like to mention quickly the easy-to-use Find Duplicates Query Wizard.
Suppose you have a table of contact info for suppliers. You want to check whether you've entered any supplier records twice. The field for supplier names doesn't allow duplicates—that is, its Indexed property is set to Yes (No Duplicates). But the field for street addresses allows duplicates—that is, its Indexed property is set to No or Yes (Duplicates OK).
If you have duplicates in the street address, it's possible that you have entered two records for the same company, using variations of the company name. It's also entirely possible that you have two different suppliers at the same street address.
This is the ...