The Find Unmatched Query Wizard helps you find the records in one table that do not have matching records in another table. For example, you could find customers who have never booked a tour.
Some scenarios when you might need to create such a query include:
To find customers who have never placed an order.
To find products that have never been purchased.
To find "orphan" records. If you haven't enforced referential integrity in your related tables, deleting a record in one table could leave one or more orphan records in a related table.
Now you need to choose the table or query whose values you want to display in the query. For example, if you ran a tour company and wanted to find customers without any tour packages, you would select the tblCustomers table.
Here you should specify the related field to join the records in the first table to the records in the second table. To do this, you need to select the same field in both lists.