#!/usr/bin/perl

use strict;
use warnings;
use Local::DBIC_Schema;

my $schema = Local::DBIC_Schema->connect( 'DBI:SQLite:pktm' );
$schema->storage->debug(1);

my $thread = $schema->resultset( 'T' )->search(
    { 'testid' => 1 },
    { 
        join      => 'Ps',
        '+select' => 'Ps.timestamp',
        '+as'     => 'timestamp',
        order_by  => 'Ps.timestamp DESC',
    }
)->first;

print $thread->get_column( 'timestamp' );