my @cols = ('field1','field2','field3');      

while ( my $row = $sth->fetchrow_arrayref ) {
    # create a hash ref to assign values to cols
    my $tmp = {};
    @$tmp{@cols} = @$row;                     
    push @xml_array, $tmp;                    
}
# Access fields like so...
print $xml_array[0]->{field1},"\n";