The solution is even easier than the other (good) suggestions in this thread. Use the new CREATE TABLE AS SELECT syntax to combine the three operations (remove a column, sum the columns, create a new table with the sums) into a single statement. This is a complete script that does exactly that, it creates a new CSV file called "partition_new.csv" with exactly the result set you specified:

#!/usr/bin/perl -w
use strict;
use DBI;
my $dbh=DBI->connect("dbi:CSV(RaiseError=1):csv_eol=\n");
$dbh->{csv_tables}->{partition}->{file}='partition.csv';
$dbh->{csv_tables}->{partition_new}->{file}='partition_new.csv';
$dbh->do("DROP TABLE IF EXISTS partition_new");
$dbh->do("
    CREATE TABLE  partition_new
       AS SELECT  colIP
               ,  SUM(colPartitionSize) AS colPartitionSize
               ,  SUM(colPartitionFree) AS colPartitionFree
            FROM  partition
        GROUP BY  colIP
");
print `cat partition_new.csv`;
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