When making ISBN search (having chosen ISBN from the menu, NOT using ccl query) Koha generates fake results - instead of using nb (@attr 1=7) index it looks for given string anywhere in records.  This is, most probably, caused by following fragment of C4::Search::buildQuery:

                # ISBN,ISSN,Standard Number, don't need special treatment
                elsif ( $index eq 'nb' || $index eq 'ns' ) {
                    $indexes_set++;
                    (
                        $stemming,      $auto_truncation,
                        $weight_fields, $fuzzy_enabled,
                        $remove_stopwords
                    ) = ( 0, 0, 0, 0, 0 );

                }

Fast workaround could be as attached at the bottom, but maybe somebody would propose a more elegant solution.

Best regards,

Janusz


--- Search.pm   2010-12-30 10:41:23.000000000 +0200
+++ /usr/share/koha/lib/C4/Search.pm    2010-12-30 10:33:35.000000000 +0200
@@ -1125,6 +1129,7 @@
                 unless ( $indexes_set || !$index || $index =~ /(st-|phr|ext|wrdl)/ ) {
                     $struct_attr = ",wrdl";
                 }
+$indexes_set = 0 if ( $index eq 'nb' || $index eq 'ns' ); 
 
                 # Some helpful index variants
                 my $index_plus       = $index . $struct_attr . ':';
@@ -1307,7 +1312,7 @@
     # This is flawed , means we can't search anything with : in it
     # if user wants to do ccl or cql, start the query with that
 #    $query =~ s/:/=/g;
-    $query =~ s/(?<=(ti|au|pb|su|an|kw|mc)):/=/g;
+    $query =~ s/(?<=(ti|au|pb|su|an|kw|mc|nb|nc)):/=/g;
     $query =~ s/(?<=(wrdl)):/=/g;
     $query =~ s/(?<=(trn|phr)):/=/g;
     $limit =~ s/:/=/g;