Empty Strings are converted to NULLs

We are developing a Java application intended to work with multiple databases. We want to store empty strings but oracle converts this to NULL values. Is there a way to tell the Oracle Database not to convert the empty string to NULL and to store it as an empty string?
Thanks
Joaquim Franco <[email protected]>
GEDI, SA

Our project started with a MySQL database and the code is full of built queries like "Select Field from table where field = var" where var can be an empty string. It would be easier for us to turn a switch in the database then to look for every query in the application and add code to test is var is empty a change the query to "Select Field from table where field is NULL".
Best Regards
Joaquim Franco
> It is a quirk of Oracle that it regards empty strings
> and NULLs as being the same thing. This behaviour
> has been built into the database forever. Oracle
> keep threatening to change but I suspect they are
> scared of the impact, not least on their own code.
> As Oracle increasingly embrace Java they may decide
> to revisit this - I don't know whether the behaviour
> is changed in 10G.
>
> What sort of problems does it cause you?
>
> Cheers, APC

Similar Messages

Oracle and empty strings

Hi All,
i'm porting my application to Oracle and i'm experiencing (big) issues since empty strings are treated as null by Oracle.
This is a big issue for me since my application uses empty and null values as two different things (indeed they are different !!), ie, i'm not having null pointer exception, but wrong behavior.
I'm thinking what's the best approach to follow since my appl. must work also on mysql and postgres.
Three options at the moment:
1. implement a jdbc wrapper that converts any empty string in something like '~'.
2. using aspectj, add some aspects to setString/getString converting any empty string in something like '~'.
3. buy a commercial driver that makes difference between empty and null (using aforementioned approaches ?).
I think that this difference in Oracle is really an impediment in doing applications db neutral and I'd like to ask your opinion about the best solution (if someone already resolved it as i guess).
Does anyone know if there are commercial jdbc driver that can help me ?
Does anyone know how ORM frameworks (like hibernate) handle this case ?
Thanks in advance
ste

jschell wrote:
nichele wrote:
jwenting wrote:
If NULL really is different in your context from an empty string you're going to have to define some sequence of characters as indicating an empty string.yes, this is what i need to implement.Sounds like a flawed design then.
I'm wondering what's the best approach in order to avoid to change all my application isolating this behavior somewhere (wrapping the jdbc driver for instance).That doesn't make much sense to me. You should already have a database layer. You change the database layer. If you don't have a database layer then that means you have another design flaw. And in that case I would really not be the one that needs to maintain that code base.I thought a bit about the value of your answer...but i didn't find it ....sorry but i don't like who replies on forum just to say bad design/bad choice etc...if you have any kind of suggestion you are welcome, otherwise you can spend your time in doing something else instead of reply to this thread.

JDBC Receiver does not convert empty string to NULL

Hello experts,
I am facing a problem with an INSERT statement to ORACLE DB where some of the fields are empty, for example:
- <STATEMENT_VLP_CONT_DETAILS>
- <TABLE_VLP_CONT_DETAILS ACTION="INSERT">
<TABLE>VLP_CONT_DETAILS</TABLE>
- <ACCESS>
<VLP_HDR_ID>43</VLP_HDR_ID>
<VLP_CONT_LINE_ID>1</VLP_CONT_LINE_ID>
<QUANTITY>1</QUANTITY>
<OWNER>CBHU</OWNER>
<SERIAL_NO>3372739</SERIAL_NO>
<CONT_ISO_CODE>2300</CONT_ISO_CODE>
<WEIGHT>6.44</WEIGHT>
<POL>ILASH</POL>
<POD>FRFOS</POD>
<FD>FRFOS</FD>
<OPER_CODE>COS</OPER_CODE>
<CUR_STOW_LOC>150102</CUR_STOW_LOC>
<PRV_STOW_LOC />
<HAZARDOUS>N</HAZARDOUS>
In the JDBC Receiver comm channel I selected: Interpretation of Empty String Values = NULL Value.
It seems the empty strings are not converted to NULL values as can be seen in the reflected SQL statement in RWB:
INSERT INTO VLP_CONT_DETAILS (VLP_HDR_ID, VLP_CONT_LINE_ID, QUANTITY, OWNER, SERIAL_NO, CONT_ISO_CODE, WEIGHT, POL, POD, FD, OPER_CODE, CUR_STOW_LOC, PRV_STOW_LOC, HAZARDOUS, EMPTY, REFER, OOG, HAZARD_IMDG, TEMP_SET, TEMP_MIN, TEMP_MAX, FRONT_OVL, REAR_OVL, RIGHT_OVW, LEFT_OVW, OVERHEIGHT, COMMODITY, BOOKING_REF, ALLOTMENT, YARD_LOC, LD_SEQ_CRANEID, LD_SEQ_NUMBER, LD_STATUS, STACKABLE, OPT_PORT_CODE1, OPT_PORT_CODE2, OPT_PORT_CODE3) VALUES (44, 1, 1, CBHU, 3372739 , 2300, 6.44, ILASH, FRFOS, FRFOS, COS, 150102, , N, N, N, N, , , , , , , , , , , , , , , 0, 64, N, , , )
So, I am getting the following error:
Could not execute statement for table/stored proc. "VLP_CONT_DETAILS" (structure "STATEMENT_VLP_CONT_DETAILS") due to java.sql.SQLException: ORA-00936: missing expression
Help would be appreciated.

Hi Effi,
There is a mismatch in the field and thier value.
Here field id 37
VLP_HDR_ID, VLP_CONT_LINE_ID, QUANTITY, OWNER, SERIAL_NO, CONT_ISO_CODE, WEIGHT, POL, POD, FD, OPER_CODE, CUR_STOW_LOC, PRV_STOW_LOC, HAZARDOUS, EMPTY, REFER, OOG, HAZARD_IMDG, TEMP_SET, TEMP_MIN, TEMP_MAX, FRONT_OVL, REAR_OVL, RIGHT_OVW, LEFT_OVW, OVERHEIGHT, COMMODITY, BOOKING_REF, ALLOTMENT, YARD_LOC, LD_SEQ_CRANEID, LD_SEQ_NUMBER, LD_STATUS, STACKABLE, OPT_PORT_CODE1, OPT_PORT_CODE2, OPT_PORT_CODE3
And value is 35
44, 1, 1, CBHU, 3372739 , 2300, 6.44, ILASH, FRFOS, FRFOS, COS, 150102, , N, N, N, N, , , , , , , , , , , , , , , 0, 64, N, , ,
Give empty values for nuil fields so that they can be made NULL by jdbc adapter
Regards
Suraj

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.

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.

[svn:bz-trunk] 11030: Tweak the deserialization of ASObjects to treat an empty string for the type of an object as null .

Revision: 11030
Author:   [email protected]
Date:     2009-10-20 11:35:02 -0700 (Tue, 20 Oct 2009)
Log Message:
Tweak the deserialization of ASObjects to treat an empty string for the type of an object as null. It appears that there is some logic in the LC remoting code that relies on a non-null class name to always exist. This change reverts to the old behavior of not allowing empty string as a value for the ASObject.namedType.
This should fix bug 2448442 and its duplicates caused by the recent serialization changes.
I don't think this is the perfect fix. Pending further investigation, a better fix would be either:
a. If it's OK to assume that empty string should always mean null for the type of the ASObject, the code that enforces it should be in the setter/getter inside ASObject and not in the deserializer.
b. ASObject doesn't guarantee that a named type exists or is valid. In that sense an empty string is as bad as some random characters that cannot be a valid class name in java, so depending on how disruptive it may be, the fix should be in any logic that uses ASObject.getType().
Modified Paths:
    blazeds/trunk/modules/core/src/flex/messaging/io/amf/AbstractAmfInput.java

Hi Pavan,
"In your payload there is no namespace prefix for the elements under PayloadHeader element."
Yes, you are right - but this message is standard AQ Adapter Header message - it's not defined by me. I just used message which was automatically added to my project when I have defined AQ Adapter.
"In your process is the default namespace is same as namespace value of tns ??"
Do you mean targetNamespace? If yes it's different as it points to process "targetNamespace="http://xmlns.oracle.com/PF_SOA_jws/PF_APPS/APPS_PROCESS" (names of application and process have changed as I try different ways to do that)
ns1 is: xmlns:ns1="http://xmlns.oracle.com/pcbpel/adapter/aq/PF_SOA/PF_APPS/PO_AQ"
"another thing is tns and ns1 should have same values.."
When I create a variable of header type, namespace ns1 is automatically created for it. I set it as property of receive activity. When process is instantiated on the serwer I get the error in which you can see that namespace is tns.
Maybe I'm doing something wrong but I don't see how I could fix this in my process.
You can see that the message I get on the server has nothing in common with the application/project/process names. Is it possible to define such variable?
Regards
Pawel
PS:
In Transformation xsl file, both variables (source and target) has tns namespace for Header and PayloadHeader, and no namespace for subfields.
Edited by: pawel.fidelus on 2010-01-05 02:37

NULL vs. Empty String

I am new to ORACLE, moving over from MS SQL Server. Is it true that you cannot enter an empty string into a NOT NULL VARCHAR2?
I am trying to convert data from an existing DB and I NEED to be able to have an empty string as much of the code base is using this to validate data (vs. a NULL). Is there any solution at all for this problem? I really do not want to keep my existing DB running but there is too much time involved converting code.
Thanks, In Advance

Bryna,
In Oracle database, Oracle treats NULL and empty string
column the same. Therefore, you cannot insert an empty string into a NOT NULL column.
In OracleDataReader, if you want to find out if the column contains the NULL values, use the OracleDataReader.IsDBNull() function.
Thanks
Martha

Null/Empty Strings use in ESB Database Adapter

Hi
I'm trying to use a database adapter to execute an update on a table with a composite primary key; one of the primary key columns sometimes contains an empty string, however whenever I try to call the adapter, it always converts this to a null value. Is there an easy way to force the adapter to use an empty string instead of a null?
Thanks.

the idea here is to execute the dbms statement, or the setpolicycontext statement in a db session, and being able to execute the next sql statement in the same db session.
This is possible with consecutive database adapters sharing the same db session.
and two db adapters sharing the same db session is possible, if you make sure that the bpel is participating in the db transaction which can be made possible via xa db connections.
Hope this helps,
Write back in case you need more info.

Varchar2, empty strings and NULL

Hi all,
When inserting an empty string into a column of type varchar2 - is a NULL value stored in the column by the database? I've seen conflicting reports, and I know that the SQL 1992 spec specifies that empty strings not be treated as a NULL value, but that Oracle has traditionally treated zero length strings stored in a varchar2 column as NULL.
So, is there a way to store an empty string in a varchar2 column as an empty string and not a NULL value?
TIA,
Seth

It can be even more complicated or annoying than NULL not equal to ASCII NULL.
example:
create table test_null
(fld1 varchar2(10),
fld2 varchar2(10),
fld3 varchar2(20));
insert into test_null values (chr(0),null, 'chr(0) and null');
insert into test_null values (null, null, 'null and null');
insert into test_null values ('', chr(0), ''''' and chr(0)');
insert into test_null values ('', null, ''''' and null');
select * from test_null;
FLD1       FLD2       FLD3
                      chr(0) and null
                      null and null
                      '' and chr(0)
                      '' and null
1 DECLARE
2 BEGIN
3   for c1 in (select fld1, fld2, fld3 from test_null) loop
4      if c1.fld1 = c1.fld2 then
5         dbms_output.put_line(c1.fld3||' Are equal'||
6                ' Length fld1 = '||to_char(length(c1.fld1))||
7                ' Length fld2 = '||to_char(length(c1.fld2)));
8      else
9         dbms_output.put_line(c1.fld3||' Are NOT equal'||
10                ' Length fld1 = '||to_char(length(c1.fld1))||
11                ' Length fld2 = '||to_char(length(c1.fld2)));
12      end if;
13      dbms_output.put_line(' ');
14   end loop;
15* END;
SQL> /
chr(0) and null Are NOT equal Length fld1 = 1 Length fld2 =
null and null Are NOT equal Length fld1 = Length fld2 =
'' and chr(0) Are NOT equal Length fld1 = Length fld2 = 1
'' and null Are NOT equal Length fld1 = Length fld2 =
PL/SQL procedure successfully completed.

Empty string == NULL ???!?!?!?!??!

Hi SQlers ...
I'm using Oracle 8.1.7 ... and Oracle maps the literal empty
string value, to the NULL value ... it that the expected result?
simple example:
SELECT 1 from dual where ('' is null)
I've tried the same on others rdbms, and of course, the
result is not the same.
thanks in advance
saludos
dario estepario ...

Yup. In Oracle the empty string '' and NULL are identical, though they periodically threaten that this may change in the future.
Justin

Empty strings morphed to NULL ???

Hi all,
I am executing the following SQL-statement (short version):
statement = (OraclePreparedStatement)
connection.prepareStatement(
"INSERT INTO TEST VALUES (?)");
statement.defineColumnType(1, OracleTypes.VARCHAR);
statement.setString (1,"");
statement.execute();
statement.close();
connection.commit();
Then I have a look into the table TEST (with SQL-PLUS) and see
that my stringValue "" morphed to a NULL-value !!!
Why are "" Strings mapped to NULL ???
Is there a configuration-parameter to turn this "feature" off ???
"" is not the same as NULL, is it ???
Thank You in advance,
Ralf.
null

Ralf Severloh (guest) wrote:
: Why are "" Strings mapped to NULL ???
This is a known Oracle feature / bug (depending on your
perspective). Null strings are equal to null. Try "SELECT 1 FROM
dual WHERE '' IS NULL;" to prove it.
: Is there a configuration-parameter to turn this "feature" off
Not as far as I know.
: "" is not the same as NULL, is it ???
Not to my way of thinking, however Oracle disagrees.
--> Steve
null

Using Convert to handle NULL values for empty Strings ""

After having had the problem with null values not being returned as nulls and reading some suggestion solution I added a converter to my application.
<converter>
    <converter-id>NullStringConverter</converter-id>
    <converter-for-class>java.lang.String</converter-for-class>
    <converter-class>com.j2anywhere.addressbookserver.web.NullStringConverter</converter-class>
</converter>
...I then implemented it as follows:
public String getAsString(FacesContext context, UIComponent component, Object object)
    System.out.println("Converting to String : "+object);
    if (object == null)
      System.out.println("READING null");
      return "NULL";
    else
      if (((String)object).equals(""))
        System.out.println("READING null (Second Check)");
        return null;
      else
        return object.toString();
public Object getAsObject(FacesContext context, UIComponent component, String value)
    System.out.println("Converting to Object: "+value+"-"+value.trim().length());
    if (value.trim().length()==0 || value.equals("NULL"))
      System.out.println("WRITING null");
      return null;
    else
      return value.toUpperCase();
...I can see that it is converting my values, however the object to which the inputText fields are bound are still set to empty strings ""
<h:inputText size="50" value="#{addressBookController.contactDetails.information}" converter="NullStringConverter"/>Also when reading the object values any nulls are already converted to empty strings before ariving at the converter. It seems that there is a default converter handling string values.
How can I resolve this problem as set nulls when the input value is an empty string other then checking every string in my class individually. I would really hate to pollute my object model with empty string tests.
Thanks in advance
Edited by: j2anywhere.com on Oct 19, 2008 9:06 AM

I changed my converter as suggested :
public Object getAsObject(FacesContext context, UIComponent component, String value)
    if (value == null || value.trim().length() == 0)
      if (component instanceof EditableValueHolder)
        System.out.println("SUBMITTED VALUE SET TO NULL");
        ((EditableValueHolder) component).setSubmittedValue(null);
      else
        System.out.println("COMPONENT :"+component.getClass().getName());
      System.out.println("Converting to Object: " + value + "< to " + null);
      return null;
    System.out.println("Converting to Object: " + value + "< to " + value);
    return value;
}which produces the following output :
SUBMITTED VALUE SET TO NULL
Converting to Object: < to null
Info : The INFO line however comes from my controller object where I print out the set value :
package com.simple;
import java.util.ArrayList;
import java.util.List;
public class Controller
private String information;
/** Creates a new instance of Controller */
public Controller()
    System.out.println("Createing Controller");
    information = "Constructed";
public String process()
    System.out.println("Info : "+getInformation());
    return "processed";
public String reset()
    setInformation("Re-Constructed");
    System.out.println("Info : "+getInformation());
    return "processed";
public String setNull()
    setInformation(null);
    System.out.println("Info : "+getInformation());
    return "processed";
public String getInformation()
    return information;
public void setInformation(String information)
    this.information = information;
}I also changes my JSP / JSF page a little. Here is the updated version
<%@page contentType="text/html"%>
<%@page pageEncoding="UTF-8"%>
<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<%@taglib prefix="f" uri="http://java.sun.com/jsf/core"%>
<%@taglib prefix="h" uri="http://java.sun.com/jsf/html"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<%--
    This file is an entry point for JavaServer Faces application.
--%>
<html>
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <title>JSP Page</title>
</head>
<body>
    <f:view>
      <h:form>
        <h:inputText id="value" value="#{Controller.information}"/>
        <hr/>
        <h:commandLink action="#{Controller.process}">
          <h:outputText id="clicker" value="Process"/>
        </h:commandLink>
        <hr/>
        <h:commandLink action="#{Controller.reset}">
          <h:outputText id="reset" value="Reset"/>
        </h:commandLink>
        <hr/>
        <h:commandLink action="#{Controller.setNull}">
          <h:outputText id="setNull" value="Set Null"/>
        </h:commandLink>
      </h:form>
    </f:view>
</body>
</html>The converter is declared for the String class in the faces configuration file. From the log message is appears to be invoked, however the object is not set to null.
I tested this with JSF 1.2_04-b20-p03 as well as 1.2_09-b02-FCS.
any other suggestions what could be causing this.

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

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.

Null or Empty string in OracleXMLQuery - XDK

Dear all,
I am using OracleXMLQuery of XDK to construct an XML File from the contents retrieved from the database.
I see that for columns which have null values or empty string, the corresponding tag is not displayed in the XML File. Instead, even for columns that have empty string I need the tags to be displayed in the following format <tag1> </tag1>
Kindly let me know if this is possible.

Ya, I will try that. That seems to be a good idea. Thanks for the response.
I have one more query. Whenever we add a new column to any table in Oracle, the column name is stored in Upper case. So when we generate XML File from the database, all the tags are either in upper case (or we can use qry.useLowerCaseTagNames() to retrieve the tag names in lower case). But the XSD contains tag names in mixed case. So when validating the XML Document against an XSD, it throws a validation error.
Is there any way I can avoid this?

Empty Strings are converted to NULLs

Similar Messages

Maybe you are looking for