You haven't shown us the whole script (maybe we should be grateful), but let me suggest the following minor additions and changes to the code that you posted -- try this out and see what happens:

#!/usr/bin/perl

use strict;
use DBI;

my $tablename = 'table_name';  # maybe this is really a file name?
my $last_col = 20; # pick a number (any number?) -- you must know the 
+right one

my $colnames = join( ',', map { sprintf( "field%d", $_ ) } 1 .. $last_
+col );
my $placehld = join( ',', map { '?' } 1 .. $last_col );

my $sql = "insert into $tablename ($colnames) values ($placehld)";

print STDERR "Ready to do:\n $sql\n";  # see how that looks

open( DATAFILE, "wheres_the_data" ) or die "wheres_the_data: $!";

my $dbh = DBI->new( blah blah );
my $insert_data = $dbh->prepare( $sql );

foreach (<DATAFILE>)
{
    chomp;
    my (@ROW) = split /,/;
    if ( @ROW != $last_col ) {
        # what do you do if the number of "fields" in ROW
        # is greater than or less than the number of columns
        # in the table?  Think about that, and do it here.
    } else {
        $insert_data->execute( @ROW );
    }
}
[download]

So there were a lot of problems with the code you posted, like using "print" where you needed to use "sprintf", not doing "chomp" on the input data file, and really misinterpreting what the DBI man page tells you about how to use placeholders.

I'm hoping that if you start with this version, you'll get what you want more easily.