gistfile1.txt

    my %kv = map {$_ => [ $args{$_}, undef ]} @fields;

    my $nullcount = join " + ", map "(me.$_ IS NULL)", @fields;

    my $min_nulls = $self->base_rs->search(
        \%kv,
        { 'select' => [ { "min" => \$nullcount } ],
      });

    my $rs = $self->base_rs->search(\%kv);

    $rs = $rs->search(
        { $nullcount =>
            { "=", $min_nulls->as_query }});

----------------------------------

SELECT me.max_payment_id, me.location_id, me.department_id, me.client_id, me.payment_channel_id, me.payment_type, me.max_payment_amount FROM max_payments me
WHERE ( ( (me.payment_channel_id IS NULL) + (me.payment_type IS NULL) + (me.client_id IS NULL) + (me.department_id IS NULL) + (me.location_id IS NULL) 
    =
    (SELECT MIN( (me.payment_channel_id IS NULL) + (me.payment_type IS NULL) + (me.client_id IS NULL) + (me.department_id IS NULL) + (me.location_id IS NULL) )
    FROM max_payments me
    WHERE ( ( ( client_id = ? OR client_id IS NULL ) AND
              ( department_id = ? OR department_id IS NULL ) AND
              ( location_id = ? OR location_id IS NULL ) AND
              ( payment_channel_id = ? OR payment_channel_id IS NULL ) AND
              ( payment_type = ? OR payment_type IS NULL ) ) )) 
AND
( ( client_id = ? OR client_id IS NULL ) AND
( department_id = ? OR department_id IS NULL ) AND
( location_id = ? OR location_id IS NULL ) AND
( payment_channel_id = ? OR payment_channel_id IS NULL ) AND
( payment_type = ? OR payment_type IS NULL ) ) ) )