Hey guys, been cracking my head trying to solve this problem.
Wondering if anyone can help me shed some light into this.

-[The Situation]-

I'm developing in Java and using firebird 1.5. I have a prepared
statement with the sql set to sth like :

1: select table1.documentno,
2: table2.refno,
3: table2.chequestatus
4: from table1,table2
5: where table2.tid = table1.tid
6: and table1.documentno = ?
7: and table2.refno = ?

the prepared statement is then fill with parameters like so:

pstmt.setString(1,variable1);
pstmt.setString(2,variable2);

The problem here happens when, sometimes, variable2 is null. when i
execute the prepared statement, it would not return any resultset. I
noticed that to get resultsets, i'd have to use the following SQL in
line 7:

" and table2.refno is null "

I tried using

pstmt.setNull(2,Types.VARCHAR);

if variable2 is null, but it still returns no resultset.


-[The Question]-

My question here is, is there a String or character in firebird that
represents NULL for the type varchar such that i am able to do a '='
operation to evaluate to a NULL value, instead of using 'is' operator?
If there isn't, anyone have a better idea instead of creating 2
prepared statements (1 more to cater for variable2 = null) ???


Thanks a million in advance!!

Regards,
Marvin