Hi, All -- We're using the following report to identify records w/ duplicate ISBNs. SELECT GROUP_CONCAT(b.biblionumber SEPARATOR ', ') AS biblionumbers, b.title, b.author, GROUP_CONCAT(i.isbn SEPARATOR ', ') AS isbns FROM biblio b LEFT JOIN biblioitems i ON (i.biblionumber=b.biblionumber) GROUP BY CONCAT(substr(b.title,0,9),"/",i.isbn) HAVING COUNT(CONCAT(substr(b.title,0,9),"/",i.isbn))>1 We're a coop, however, so it would be helpful to limit the results to cases where our particular library owns at least one of the associated items. Adding the following lines did not provide correct results, unfortunately: LEFT JOIN items m ON (m.biblionumber=b.biblionumber) WHERE m.homebranch = <<Library|branches>> I suspect a subquery may be required, but it's beyond my current proficiency w/ MySQL :-( Thanks in advance for any guidance. All best, Cab Vinton, Director Plaistow Public Library Plaistow, NH