# Map the column name to the validator code:
my %validator = (
    P_12MONTHDEMANDQTY => \&validate_number,
    ...
    P_DLRUOM => \&validate_p_dlruom,
    ...
);

sub validate_fields
{
    my ($updateval, $colname) = @_;
    if (! exists $validator{ $colname }) {
        warn "'$colname' is not a valid column name.";
    };
    my $code = $validator{ $colname };
    if (! $code->($updateval, $colname)) {
        warn "'$updateval' is not a valid value for '$colname'.";
    } else {
        warn "'$updateval' is a valid value for '$colname'.";
        return 1
    };
}