>How would you insure that the entries in a given field are unique OR blank? That is, multiple blank records are OK but if data is entered, it must be a unique value. Setting up a candidate index doesn't work due to the blank fields.

SELECT cField, CNT(*) AS nCnt ;
FROM YourTable ;
WHERE NOT EMPTY(cField) ;
GROUP BY cField ;
HAVING nCnt > 1 ;
INTO CURSOR Dups

This gives you a list of duplicate values.

Tamar