XMLType in oracle not generating tags for columns with Null values

I am trying to Convert the below table rows to XMLtype and then to clob

ID, PROJ_NO
1   Proj1
2   (null)
3   Proj5

I used the below Query to convert each row to xml

 select xmltype( cursor(Select * from PROJ_TEST_DEMO where id= 1  )).getclobval() from  dual

Result is

"<?xml version="1.0"?>
<ROWSET>
 <ROW>
  <ID>1</ID>
  <PROJ_NO>Proj1</PROJ_NO>
 </ROW>
</ROWSET>
"

While

select xmltype( cursor(Select * from PROJ_TEST_DEMO where id=3  ) ).getclobval() from  dual

gives

"<?xml version="1.0"?>
<ROWSET>
 <ROW>
  <ID>3</ID>
 </ROW>
</ROWSET>
"

Is there a option to stop xmltype from excluding null value columns

Solution

You can use dbms_xmlgen with dbms_xmlgen.setNullHandling(qryCtx, dbms_xmlgen.EMPTY_TAG) or dbms_xmlgen.NULL_ATTR:

For example, create own function

create or replace function f_get_xmltype_with_nulls (cur sys_refcursor, null_handling int default dbms_xmlgen.null_attr)
  return xmltype
as
  /* null_handling may be: 
      DROP_NULLS CONSTANT NUMBER:= 0;  Leaves out the tag for NULL elements.
      NULL_ATTR CONSTANT NUMBER:= 1; (Default) Sets xsi:nil="true".
      EMPTY_TAG CONSTANT NUMBER:= 2; Sets, for example, <foo/>.
  */
  res xmltype;
  lc dbms_xmlgen.ctxhandle;
begin
  lc:=dbms_xmlgen.newcontext(cur);
  -- you can replace null_attr with empty_tag here:
  dbms_xmlgen.setnullhandling(lc, null_handling);
  res:=dbms_xmlgen.getxmltype(lc);
  return res;
end;
/

then you can use it in queries:

SQL> select f_get_xmltype_with_nulls(cursor(select null x from dual connect by level<10)) x from dual;

X
------------------------------------------------------------------------
<ROWSET xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance">
 <ROW>
  <X xsi:nil = "true"/>
 </ROW>
 <ROW>
  <X xsi:nil = "true"/>
 </ROW>
 <ROW>
  <X xsi:nil = "true"/>
 </ROW>
 <ROW>
  <X xsi:nil = "true"/>
 </ROW>
 <ROW>
  <X xsi:nil = "true"/>
 </ROW>
 <ROW>
  <X xsi:nil = "true"/>
 </ROW>
 <ROW>
  <X xsi:nil = "true"/>
 </ROW>
 <ROW>
  <X xsi:nil = "true"/>
 </ROW>
 <ROW>
  <X xsi:nil = "true"/>
 </ROW>
</ROWSET>

As you can see second parameter of this function is null_handling:

DROP_NULLS CONSTANT NUMBER:= 0; Leaves out the tag for NULL elements.
NULL_ATTR CONSTANT NUMBER:= 1; (Default) Sets xsi:nil="true".
EMPTY_TAG CONSTANT NUMBER:= 2; Sets, for example, .

Or you can even inline your function into the query:

with 
   function f_get_xmltype_with_nulls (cur sys_refcursor, null_handling int default dbms_xmlgen.null_attr)
     return xmltype
   as
     /* null_handling may be: 
         DROP_NULLS CONSTANT NUMBER:= 0;  Leaves out the tag for NULL elements.
         NULL_ATTR CONSTANT NUMBER:= 1; (Default) Sets xsi:nil="true".
         EMPTY_TAG CONSTANT NUMBER:= 2; Sets, for example, <foo/>.
     */
     res xmltype;
     lc dbms_xmlgen.ctxhandle;
   begin
     lc:=dbms_xmlgen.newcontext(cur);
     -- you can replace null_attr with empty_tag here:
     dbms_xmlgen.setnullhandling(lc, null_handling);
     res:=dbms_xmlgen.getxmltype(lc);
     return res;
   end;
select
   f_get_xmltype_with_nulls(cursor(select null as x from dual)) as xxx 
from dual
/

Result with default NULL_ATTR:

XXX
-----------------------------------------------------------------
<ROWSET xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance">
 <ROW>
  <X xsi:nil = "true"/>
 </ROW>
</ROWSET>

Result with default EMPTY_TAG:

select
   f_get_xmltype_with_nulls(cursor(select null as x from dual),2) as xxx 
from dual;

XXX
-------------------------------------
<ROWSET>
 <ROW>
  <X/>
 </ROW>
</ROWSET>