my $sth = $db->prepare( "describe my_big_table" );
$sth->execute;

my $rows = $sth->fetchall_arrayref;
$sth->finish;

my @column_names = map { $$_[0] } @$rows;

my $insert_sql =
    join( '',
	  'insert into my_big_table (',
	  join( ',', @column_names ),
	  ') values (',
	  join( ',', ( '?') x scalar @column_names ),
	  ')'
    );

# check your work, if you like:
print join( "\n", "=== columns:", @column_names, '=== sql:', $insert_sql, '' );