Null and empty string not being the same in object?

Hello,
I know that null and empty string are interpreted the same in oracle.
However I discovered the strange behaviour concerning user defined objects:
create or replace
TYPE object AS OBJECT (
value VARCHAR2(2000)
declare
xml xmltype;
obj object;
begin
obj := object('abcd');
xml := xmltype(obj);
dbms_output.put_line(xml.getStringVal());
obj.value := '';
xml := xmltype(obj);
dbms_output.put_line(xml.getStringVal());
obj.value := null;
xml := xmltype(obj);
dbms_output.put_line(xml.getStringVal());
end;
When creating xml from object, all not-null fields are transformed into xml tag.
I supposed that obj.value being either '' or null will lead to the same result.
However this is output from Oracle 9i:
<OBJECT_ID><VALUE>abcd</VALUE></OBJECT_ID>
<OBJECT_ID><VALUE></VALUE></OBJECT_ID>
<OBJECT_ID/>
Oracle 10g behaves as expected:
<OBJECT><VALUE>abcd</VALUE></OBJECT>
<OBJECT/>
<OBJECT/>
However Oracle 9i behaviour leads me to the conclusion that oracle
must somehow distinguish between empty string and null in user defined objects...
Can someone clarify this behaviour?
Thus is it possible to test if object's field is empty or null?

However Oracle 9i behaviour leads me to the conclusion that oracle
must somehow distinguish between empty string and null in user defined objects...
Can someone clarify this behaviour?
Thus is it possible to test if object's field is empty or null?A lot of "fixes" were done, relating to XML in 10g and the XML functionality of 9i was known to be buggy.
I think you can safely assume that null and empty strings are treated the same by Oracle regardless. If you're using anything less than 10g, it's not supported any more anyway, so upgrade. Don't rely on any assumptions that may appear due to bugs.

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Difference in Null and Empty String

Hi,
I have been wondering about the difference between Null and Empty String in Java. So I wrote a small program like this:
public class CompareEmptyAndNullString {
     public static void main(String args[]) {
          String sNull = null;
          String sEmpty = "";
          try {
               if (sNull.equalsIgnoreCase(sEmpty)) {
                    System.out.println("Null and Empty Strings are Equal");
               } else {
                    System.out.println("Null and Empty Strings are Equal");
          } catch (Exception e) {
               e.printStackTrace();
This program throws Exception: java.lang.NullPointerException
     at practice.programs.CompareEmptyAndNullString.main(CompareEmptyAndNullString.java:10)
Now if I change the IF Clause to if (sEmpty.equalsIgnoreCase(sNull)) then the Program outputs this: Null and Empty Strings are Equal
Can anyone explain why this would happen ?
Thanks in Advance !!

JavaProwler wrote:
Saish,
Whether you do any of the following code, the JUnit Test always passes: I mean he NOT Sign doesnt make a difference ...
assert (! "".equals(null));
assert ("".equals(null));
You probably have assertions turned off. Note the the assert keyword has nothing to do with JUnit tests.
I think that older versions of JUnit, before assert was a language keyword (which started in 1.4 or 1.5), had a method called assert. Thus, if you have old-style JUnit tests, they might still compile, but the behavior is completely different from what it was in JUnit, and has nothing to do with JUnit at all.
If you turn assertions on (-ea flag in the JVM command line, I think), the second one will throw AssertionError.

VARCHAR2:: How to differnciate between NULL and empty string '' ?

Hello to all,
I'm looking for a possibility to differnciate between NULL and empty string '' in column of type VARCHAR2.
I have an application relying on that there is a difference between NULL and ''.
Is it possible to configure ORACLE in some way ?
Thanx in advance,
Thomas

try check if a varchar variable has an empty string
by checking its lengthAnd that would accomplish what? But see for yourself:
DECLARE
v_test VARCHAR2(10);
BEGIN
v_test := '';
DBMS_OUTPUT.put_line(LENGTH(v_test));
v_test := NULL;
DBMS_OUTPUT.put_line(LENGTH(v_test));
END; C.

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Oracle, Null and empty Strings

Currently I'm facing problems with a class, which contains a String, which
is set to "" (empty String).
When the class is persistent, oracle writes null to the table column
(which seems to be common oracle behaviour) and when retrieving the class,
the field is set to null as well, giving me a lot of null-pointer
exceptions.
Anyway ... I can cope with that (just a lot of extra work)
far worse is the problem, wenn searching objects, that have this field set
to "" oder null.
Oracle can't find the records because JDO creates Querys "where
string=null" or "where string=''" , where oracle expects "where string is
null" to find the records.
Is there a workaround or solution ?

Yeah, that would work as well, thx, but since I have to cope with
null-Strings now everywhere in my program, it doesn't hurt just to forbid
empty strings on the program side.
In future times I'll test on Oracle first, then porting to DB/2 - this way
I suppose work is far less to garant compability.
Nevertheless ... having to set the bankcode into quotes is a kodo bug in
my opinion.
Kodo knows the type of classfields (in this case string) and shouldn't
send the parameter as a BigDecimal to the database.
Given that, and having only bankcodes of null (only neccesary when using
Oracle), the method would look like:
public Collection getAccounts (String bankCode)
throws Exception
return getAccounts (Account.class, "bankcode=="+bankcode);
which is how a transparent persistent layer, um, should be , um , I mean
... just transparent ;-D
Marc Prud'hommeaux wrote:
Stefan-
Couldn't you just do something like:
public Collection getAccounts (String bankCode)
throws Exception
String filter;
if (bankCode == null || bankCode.length () == 0)
filter = "(bankCode == null || bankCode == "")";
else
filter = "bankCode == "" + bankCode + """;
return getAccounts (Account.class, filter);
If I understand the problem correctly, this should work for all the
databases.
In article <[email protected]>, Stefan wrote:
What operations are you performing to cause this SQL to be issued? You
say you are having trouble removing objects, but this is clearly not a
DELETE statement. Is this the SQL that is issued when looking up
objects by identity?I'm not removing objects, I was removing just quotes from parameters ;-)
A string column... is it also represented as a string field in your class?Yeah ... just to give you an impression of the code:
First we have a class, representing a bank account:
public class Account {
private AccountMgr myAccountMgr;
private String bankCode;
private String id;
Note, that in nearly all cases bankCode will be a number or null.
I have a second class "AccountMgr", which does all of the persistant stuff
(seaching, making persistent etc.)
This class has two methods, one versatile (protected) to retrieve accounts
by a given filterString and one who just returns accounts by bankCode,
building the expected filterstring. Here is my current working version:
public class AccountMgr {
public Collection getAccounts(String bankCode) throws Exception {
if (bankCode!=null) {
if (bankCode.equals("")) {
throw new Exception("check code, bankCode='' not allowed to get
same behavior from DB2 and Oracle");
// if set, quote the bankCode
bankCode="""+bankCode+""";
return getAccounts(Account.class,"bankCode=="+bankCode);
protected Collection getAccounts(Class accountClass, String filterAdd)
throws Exception {
PersistenceManager pm = MyHelper.getPersistenceManager();
String filter="";
if (filterAdd!=null && !filterAdd.trim().equals("")) {
filter+=filterAdd + " && ";
filter += "myAccountMgr==_accMgr";
Query query = pm.newQuery(accountClass, filter);
query.declareParameters("AccountMgr _accMgr");
return (Collection) query.execute(this);
As you can see, in the first method I have to set the bankCode into
quotes, when it's not null.
This is because otherwise a filter like "bankCode=1234" will be translated
in a way, where 1234 is send as a BigDecimal to the database:
[...] executing statement <4239745>: (SELECT [...] FROM JDO_ACCOUNT t0
WHERE t0.BANKCODE = ? : [reused=1;params={(BigDecimal) 1234}]
Marc Prud'hommeaux [email protected]
SolarMetric Inc. http://www.solarmetric.com

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How to distinguish NULL and Empty Strings

Hi,
Just to set the context right; I'm an experienced C programmer trying labview for the first time. As such I ran in to a problem being that Labview has no concept of NULL-pointers and more specifically appears to have no concept of the difference between a NULL-string and an empty-string
I'm trying to make a structure (bundle) of strings (in it's most basic form key-value pairs) which i'd like to (for instance) URI encode in order to send it to a web server. For those who are not familiar with URI encoding; there is a distinguished difference between setting a key to an empty string and setting a key with no value. In C I would use a pointer to an empty string vs a NULL string pointer to symbolize this.
In essence I need an elegant way to distinguish between a defined but empty string and an undefined string (hmmm this is actually describing the same problem but now in terms of perl).
Anybody have any pointers (pun not intended) for me ?

This is a bit depending on the interface you have with your encoder. The whole issue is that LV has no pointers at all (and you will like it, as you will never have any Null-Pointer exeptions and the like).
Assuming that you use a dll (so the Call Library node).
Use CString as input -> NULL-Terminated String.
Use I32 as input and pass 0 -> NULL string.
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www.aescusoft.de
My latest community nugget on producer/consumer design
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NULL and Empty String

Hi There,
As far as I know, Null is not the same as an empty string; however, when I try this out, I get some unexpected results (well, at least unexpected for my liking):
SQL> CREATE TABLE TS (MID NUMBER,
2 MDESC VARCHAR2(20) DEFAULT '' NOT NULL);
Table created.
SQL> INSERT INTO TS VALUES(1,'');
INSERT INTO TS VALUES(1,'')
ERROR at line 1:
ORA-01400: cannot insert NULL into ("TT"."TS"."MDESC")So, according to the above scenario, I can't insert an empty string!! However, an empty string is a valid string that doesn't have tuples/data!!
How come Oracle translates the null string '' as NULL?
Thanks

William Robertson wrote:
There is a special case to do with CHAR values, whereby '' counts as a string and so gets blank-padded, whereas NULL does not.Are you referring to:
SQL> DECLARE
2      flag CHAR(2);
3      PROCEDURE check_null (p_flag IN CHAR)
4      IS
5      BEGIN
6        IF p_flag = ' '
7        THEN
8          dbms_output.put_line ('flag is equal to '' ''');
9        ELSIF p_flag IS NULL
10        THEN
11          dbms_output.put_line ('flag is null');
12        ELSE
13          dbms_output.put_line ('other');
14        END IF;
15      END;
16    BEGIN
17      flag := '';
18      check_null (flag);
19      flag := NULL;
20      check_null (flag);
21    end;
22 /
flag is equal to ' '
flag is null
PL/SQL procedure successfully completed.
SQL> alter session set events '10932 trace name context forever, level 16384';
Session altered.
SQL> DECLARE
2      flag CHAR(2);
3      PROCEDURE check_null (p_flag IN CHAR)
4      IS
5      BEGIN
6        IF p_flag = ' '
7        THEN
8          dbms_output.put_line ('flag is equal to '' ''');
9        ELSIF p_flag IS NULL
10        THEN
11          dbms_output.put_line ('flag is null');
12        ELSE
13          dbms_output.put_line ('other');
14        END IF;
15      END;
16    BEGIN
17      flag := '';
18      check_null (flag);
19      flag := NULL;
20      check_null (flag);
21    end;
22 /
flag is null
flag is null
PL/SQL procedure successfully completed.
SQL> SY.
P.S. Don't ask me why normal (or at least consistent) behavior is not the default.

More Fun with NULLs and Empty Strings

Greetings,
I ran across this behavior recently and thought I'd share with the forum. I'm running 10.2.0.2. Note the difference in behavior between passing and explicit NULL in the parameter vice passing an empty string (''):
CREATE OR REPLACE PROCEDURE NULL_ES_TEST(PARAM1 IN VARCHAR2) IS
VAR1 CHAR(1);
BEGIN
IF PARAM1 IS NULL THEN
DBMS_OUTPUT.PUT_LINE('PARAM1 IS NULL');
END IF;
VAR1 := PARAM1;
IF VAR1 IS NULL THEN
DBMS_OUTPUT.PUT_LINE('VAR1 IS NULL');
ELSE
DBMS_OUTPUT.PUT_LINE('VAR1 IS NOT NULL');
END IF;
DBMS_OUTPUT.PUT_LINE('THE LENGTH OF VAR1 IS '||TO_CHAR(LENGTH(VAR1)));
END NULL_ES_TEST;
EXEC NULL_ES_TEST(PARAM1 => '');
PARAM1 IS NULL
VAR1 IS NOT NULL
THE LENGTH OF VAR1 IS 1
(var1 now holds a single space)
EXEC NULL_ES_TEST(PARAM1 => NULL);
PARAM1 IS NULL
VAR1 IS NULL
THE LENGTH OF VAR1 IS
Any Comments or Insights are welcome.
Sincerely,
Dale Ward

Well somethings not as expected (tested on 10.2.0.3)
Even if you default the parameter to '', it treats null and '' differently.
SQL> ed
Wrote file afiedt.buf
1 CREATE OR REPLACE PROCEDURE NULL_ES_TEST(PARAM1 IN VARCHAR2 := '') IS
2    VAR1 CHAR(1);
3 BEGIN
4    IF PARAM1 IS NULL THEN
5      DBMS_OUTPUT.PUT_LINE('PARAM1 IS NULL');
6    END IF;
7    VAR1 := PARAM1;
8    IF VAR1 IS NULL THEN
9      DBMS_OUTPUT.PUT_LINE('VAR1 IS NULL');
10    ELSE
11      DBMS_OUTPUT.PUT_LINE('VAR1 IS NOT NULL');
12    END IF;
13    DBMS_OUTPUT.PUT_LINE('THE LENGTH OF VAR1 IS '||TO_CHAR(LENGTH(VAR1)));
14* END NULL_ES_TEST;
SQL> /
Procedure created.
SQL> exec null_es_test(null);
PARAM1 IS NULL
VAR1 IS NULL
THE LENGTH OF VAR1 IS
PL/SQL procedure successfully completed.
SQL> exec null_es_test('');
PARAM1 IS NULL
VAR1 IS NOT NULL
THE LENGTH OF VAR1 IS 1
PL/SQL procedure successfully completed.
SQL>

Nulls and Empty Strings

I have an ODBC application whose backend has been changed from Access to Oracle. There is one particular query that is causing problems. The query contains a where clause with something like "field = ''" in it. This query is intended to pick up records where field is null. If the query was modified to "field is null," it would work. However, I cannot change the application.
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will show you only those rows in someTable where column is non-NULL and where its value is not 'value'
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select count(*) from someTable where column = 'value'
select count(*) from someTable =
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Null and empty string not being the same in object?

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