print "\nTesting no placeholders, no results $dsn\n";
my $sth = $dbh->prepare("select 'test' where 1=0");
print Dumper $dbh->selectall_arrayref($sth);

print "\nTesting placeholders with results $dsn\n";
my $sthSecond = $dbh->prepare("select ? where 1=1");
print Dumper $dbh->selectall_arrayref($sthSecond);

print "\nTesting placeholders with no results $dsn\n";
my $sthThird = $dbh->prepare("select ? where 1=0");
print Dumper $dbh->selectall_arrayref($sthThird);
[download]

Testing no placeholders, no results dbi:Sybase:server=xxx.xxx.xxx.xxx
$VAR1 = [];

Testing placeholders with results dbi:Sybase:server=xxx.xxx.xxx.xxx
$VAR1 = [
          [
            undef
          ]
        ];

Testing placeholders with no results dbi:Sybase:server=xxx.xxx.xxx.xxx
$VAR1 = [];

Testing no placeholders, no results dbi:Sybase:server=xxx.xxx.xxx.xxx;
+tdsLevel=CS_TDS_495
$VAR1 = [];

Testing placeholders with results dbi:Sybase:server=xxx.xxx.xxx.xxx;td
+sLevel=CS_TDS_495
$VAR1 = [
          [
            undef
          ]
        ];

Testing placeholders with no results dbi:Sybase:server=xxx.xxx.xxx.xxx
+;tdsLevel=CS_TDS_495
(hang)
[download]

I'd be worried if it didn't produce the same result.

I was surprised to read this in DBD::Sybase, might be your client lib:

>DBD::Sybase supports the use of ? placeholders in SQL statements as long as the underlying library and database engine supports it. It does this by using what Sybase calls Dynamic SQL. The ? placeholders allow you to write something like: ...

When you use ? placeholders Sybase goes and creates a temporary stored procedure that corresponds to your SQL statement. You then pass variables to $sth->execute or $dbh->do, which get inserted in the query, and any rows are returned.

So ... Sybase is obviously very different from the usual SQL standard ...