use DateTime::Format::SQLite;

@ts = (
		'2009-09-20 09:10:15',
		'2009-09-21 09:10:15',
		'2009-09-22 09:10:15',
		'2009-09-23 09:10:15',
		'2009-09-24 09:10:15',
		'2009-09-25 09:10:15',
		'2009-09-26 09:10:15',
		);

foreach my $ts (@ts) {
	my ($dt, $dow);
	$dt = DateTime::Format::SQLite->parse_datetime($ts);
	$dow = $dt->day_of_week;
	$dt->add(days => (1 - $dow));
	print $dt->ymd('-');
	print "\n";
}