#!/usr/bin/perl

use warnings;
use strict;

update_table( 'test_name', 'test_phone',
              'test_city', 'test_country' );

update_table( 'test_name', 'test_phone',
              '', 'test_country' );

update_table( 'test_name', '',
              'test_city', '' );

sub update_table {
    my ($name, $phone, $city, $country) = @_;

    my $sql = qq! UPDATE table SET !
            . qq! phone = '$phone', !
            . qq! city = '$city', !
            . qq! country = '$country' !
            . qq! WHERE name = '$name' !;

    print $sql;
    return 1;
}

##</code><code>##

UPDATE table SET phone = 'test_phone', 
  city = '', country = 'test_country' FROM ...

##</code><code>##

UPDATE table SET phone = 'test_phone', 
  country = 'test_country' FROM ...