Hi Sandy_Bio_Perl,

I think that the problem isn't with the IS NOT NULL, but rather with the division on the column with the null value. Here's something I scratched together that works. Note the IFNULL in your SQL statement, as well as csv_null => 1 in the connection parameters:

#!/usr/bin/perl

use strict;
use warnings;
use DBI;

sub RunSqlSearch;


my $spreadsheet = 'newCsv.csv'; 
my $query 
    = "SELECT sid,genotype, dnabl, dnatw12 "
    . "FROM $spreadsheet "
    . "WHERE genotype = 'a' "
    . "AND (IFNULL(dnatw12,0)/dnabl)<0.5 "
    . "AND dnatw12 IS NOT NULL "
    ;   
my ($queryResult) = RunSqlSearch($query);
print "Your query $query returned the following result:\n$queryResult\
+n";

sub RunSqlSearch($){
    
    my $query = $_[0]; 
    
    # error check #
    if ($query eq ""){die "From runSqlQuery2 -  No value entered for $
+query $!\n";}
        
    # Connect to the database, (the directory containing our csv file(
+s))
    my $dbh = DBI->connect ("dbi:CSV:", undef, undef, {
        f_dir            => ".",
        f_encoding       => "utf-8",
        csv_eol          => "\n",
        csv_null         => 1,
        RaiseError       => 1,
        }) or die $DBI::errstr;
    
    # Output using sql query #
    my $sth = $dbh->prepare($query);
    $sth->execute;
    
    my @row;
    my $queryResult="";
    while (@row = $sth->fetchrow_array) {
        $queryResult .= join("\t",@row) . "\n";
    }  
        
    # output arguments #
    if ($queryResult eq ""){$queryResult = "No result found";}
    return ($queryResult);
}
[download]

Hope that points you in the right direction.

-bmt

UPDATE: Note that this will still blow up if dnabl is NULL. I played around a bit, but the IFNULL that worked in the numerator of the division failed to work in the denominator. Not sure why...