On Wed, 15 Aug 2018 09:43:50 -0400 Cab Vinton <bibliwho@gmail.com> wrote:
Figured a subquery would work as a way to first restrict the results to records where Branch A owns at least one copy, & then to perform the search for duplicate records on the resulting subset.
Oh I see. So do you mean something like SELECT GROUP_CONCAT(b.biblionumber SEPARATOR ', ') AS biblionumbers, b.title, b.author, GROUP_CONCAT(i.isbn SEPARATOR ', ') AS isbns FROM biblio b WHERE b.biblionumber IN (SELECT m.biblionumber FROM items m WHERE m.homebranch = <<Library|branches>> ) 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 ? That's probably horribly inefficient and I've not tested it because I suspect I've still misunderstood. Hope that helps, -- MJR http://mjr.towers.org.uk/ Member of http://www.software.coop/ (but this email is my personal view only)