$sth_dates_uniq = $dbh->prepare("select distinct cast(date as date) from myschema.mytable;") or die;
$sth_dates_uniq->execute();

my @all_rows;
while ( my $ref = $sth_dates_uniq->fetchrow_arrayref()) {
	push(@all_rows, $ref);
}
foreach my $row_ref (@all_rows) {
	print "@{$row_ref}\n";
}

# Output
2019-09-19
2019-09-19
2019-09-19