This is a SQL query that can be used to create a Koha report. It lists all records that simultaneously contain a principal author in fields 100, 110 and/or 111, which is just not right in MARC21.

SELECT biblionumberurl as biblionumber,title FROM
(SELECT CONCAT('<a href="http://',
              (SELECT value FROM systempreferences WHERE variable='staffClientBaseURL'),
              '/cgi-bin/koha/catalogue/detail.pl?biblionumber=',
              biblionumber,
              '">',
              biblionumber,
              '</a>') AS 'biblionumberurl', biblionumber
FROM biblioitems
WHERE
    (ExtractValue(biblioitems.marcxml,'//datafield[@tag="100"]/subfield[@code="a"]')<>'' AND
     ExtractValue(biblioitems.marcxml,'//datafield[@tag="110"]/subfield[@code="a"]')<>'' AND
     ExtractValue(biblioitems.marcxml,'//datafield[@tag="111"]/subfield[@code="a"]')<>'')
OR
    (ExtractValue(biblioitems.marcxml,'//datafield[@tag="100"]/subfield[@code="a"]')<>'' AND
     ExtractValue(biblioitems.marcxml,'//datafield[@tag="110"]/subfield[@code="a"]')<>'')
OR
    (ExtractValue(biblioitems.marcxml,'//datafield[@tag="110"]/subfield[@code="a"]')<>'' AND
     ExtractValue(biblioitems.marcxml,'//datafield[@tag="111"]/subfield[@code="a"]')<>'')
OR
    (ExtractValue(biblioitems.marcxml,'//datafield[@tag="100"]/subfield[@code="a"]')<>'' AND
     ExtractValue(biblioitems.marcxml,'//datafield[@tag="111"]/subfield[@code="a"]')<>'')
) url
LEFT JOIN
(SELECT biblionumber,title
FROM biblio
) tit
ON (url.biblionumber=tit.biblionumber)