my $nn;
my $vn = Paul;
my $array_ref = [ 	[ qw( id nachname vorname ) ],  
			[ 1, 'Lohan', 'Lindsay' ], 
			[ 2, undef, 'Karl' ], 	# gut
			[ 3, $nn, $vn ], 	# auch gut
			[ 4, ,'Peter' ],	# nicht gut	
];

$dbh->do( "CREATE TEMP TABLE $table AS import( ? )", {}, $array_ref );