my $data = [
    { col1 => 'data1', col3 => 'data3' },
    { col2 => 'data2', col3 => 'data3plus' },
];
if( ! @columns ) {
	# Collect all (potential) columns we want to write
	my %columns;
	for( @$data ) {
		$columns{ $_ } = 1
			for keys %$_;
	}
	@columns = sort keys %columns;
};

my $columns = join ",", map { qq("$_") } @columns;
my $placeholders = join ",", ("?") x @columns;

# Run the insert statement for each row in our list
my $sql_insert = qq(insert into "$table" ($columns) values ($placeholders));