[Koha-devel] How can I improve this report?

Report: Authors not in Authorities SELECT DISTINCT(author) AS heading FROM biblio WHERE author NOT IN (SELECT ExtractValue(marcxml,'//datafield[@tag="100"]/subfield[@code="a"]') AS heading FROM auth_header WHERE authtypecode='PERSO_NAME')ORDER BY heading I am not a SQL expert, but I believe this is doing an unkeyed troll through every authority record for every biblio (O(Nbibs * Mauths), which is pretty bad). I suspect we can do better by trolling Auths once to create a set and then compare Bib authors against it. How can we do this? -Doug-