Let's try this the old fashioned way ...

my $sql = qq/
SELECT id
FROM   Areas
WHERE  areaname = ?
/;

my $sth = $dbh->prepare( $sql ) or print "DB err: " . DBI->errstr;

my $rv = $sth->execute( 'BUFFALO' ) or print DBI->errstr;
my @rows  = $sth->fetchrow_array  or print DBI->errstr;
print "Try BUFFALLO, got id is: @rows \tRV was: $rv\n";


$rv = $sth->execute( undef )  or print "exec undef " . DBI->errstr;
@rows  = $sth->fetchrow_array  or print "No Rows!\n " . DBI->errstr;
print "Try undef, got id is: @rows  \tRV was: $rv \n";

$sth->finish;

$sql = qq/
SELECT id
FROM   Areas
WHERE  areaname is null 
/;

$sth = $dbh->prepare( $sql ) or print "DB err: " . DBI->errstr;
$rv = $sth->execute()  or print "exec undef " . DBI->errstr;
@rows  = $sth->fetchrow_array  or print "fetch " . DBI->errstr;
print "Try areaname is null in sql, got id is: @rows  \tRV was $rv\n";

$sth->finish;
[download]

This gives....

Try BUFFALLO, got id is: 23     RV was: 0E0
No Rows!
 Try undef, got id is:          RV was: 0E0 
Try areaname is null in sql, got id is: 1       RV was 0E0
[download]

So this shows that DBI doesn't treat undef like NULL in bindings when selecting from a dB. This is explained in the docs for DBI:

SELECT description FROM products WHERE product_code = ?
Binding an undef (NULL) to the placeholder will not select rows which have a NULL product_code! Refer to the SQL manual for your database engine or any SQL book for the reasons for this. To explicitly select NULLs you have to say "WHERE product_code IS NULL" and to make that general you have to say:
... WHERE (product_code = ? OR (? IS NULL AND product_code IS NULL)) and bind the same value to both placeholders.

Which is all well and good in set theory, but a PITA in my real world.

Class::DBI, if it is to be useful, is supposed to abstract such messiness away, IMHO.

How does one get around this while using C::DBI?