my $inputfile = "file.txt";

 my $dbh = DBI->connect("dbi:Pg:dbname=db;host=dbhost", 
			   "user", "passwd", {AutoCommit => 1});

    unless (open(INPUT, "$inputfile"))
    {
	print "ERROR: Can't open file for reading : $!\n";

    }

    while(<INPUT>)
    {

	# splitting on tab character

	my @data = split("\t", $_);

	# assigning varables

	my $did1 = $data[0];
	my $did2 = $data[1];
	my $score1 = $data[2];
	my $score2 = $data[3];
	
	if(($score1 >=70) && ($score2 >=60))
	{
	    	    	        
	    my $sth1 = $dbh->prepare("select d_id, c_id from d where d_id = '$did1';");
	    
	    $sth1->execute();
	    
	    my $sth2 = $dbh->prepare("select d_id, c_id from d where d_id = '$did2';");
	    
	    $sth2->execute();
	    
	    my $array_ref1 =  $sth1->fetchall_arrayref();

	    my $array_ref2 =  $sth2->fetchall_arrayref();

	    foreach my $row1(@$array_ref1)
	    {
		my ($did1, $cid1) = @$row1;		 

		foreach my $row2(@$array_ref2)
		{
		    my ($did2, $cid2) = @$row2;

		    if($cid2 != $cid1)
		    {
			print "$did1, $did2,  $cid1, $cid2\n";
		    }
		}
	    }
    
	}
	
    }

    close(INPUT);
    
}

##</code><code>##

A34253	S43154	70	67	
C31243	C31243	70	73	
Y54231	W65313	70	71
U65242	B65231	70	70	
Z23154	Z23154	70	65