my @where;
my @values;
my $sql = 'select * from table';

if defined $var1 { push @where, 'column1 = ?'; push @values, $var1; }
if defined $var2 { push @where, 'column2 = ?'; push @values, $var2; }
if defined $var3 { push @where, 'column3 = ?'; push @values, $var3; }

$sql = $sql . ' where ' . join(' and ', @where);

my $sth = $dbh->prepare_cached($sql);
$sth->execute(@values);