Doing a search only gives you 2 options: must match all or must match one or more.  How about one but not another?

This can get tricky because when originally selecting the fields to search for, you can only select a field once.

Here is the trick

Step 1: After configuring the first part of the search, click the add fields button again.

Step 2: Select the same field but this time, select the opposite value(s). 

Step 3: When you get back to the search screen, select the field in step 2 and select the not equal option

Step 4: Select must match all in the Search Condition area.

This will search for one, but not the other.

Here’s an example:
You want to search the Escona database for companies who deal in White wines only.  I made a UDF called “Type of Wine”.  I assigned both Red and White wine to ABC Wine Shop.  I assigned White to Wines Are Us.

So we want to retrieve all companies who deal only in White wine.  So a successful search would bring back only Wines Are Us.
So go to search> all fields.  Find the Type of Wine user-defined field and select white.  Hit ok.  You should get this following screen:

 
Then, hit the Add button again and find the Type of Wine user-defined field again. 
This time, select red.  Hit OK.

When you get back to the Search By All Fields dialog, highlight the Type of Wine = Red line and then press the “not equal” button. Also, make sure that “Must match all” is selected.  That way, it will look for both Type of Wine equal to White and Type of Wine not equal to Red.

So the end search should look something like this (sans the red highlights)