Using dblinks to access CLOB datatype

Question

Hi ,
I am using dblink to access data data from remote database. I need to access data form a table on remote database which have fields of type VARCHAR2 and CLOB. Since I can't access CLOB data directly through dblinks, i created a view for that CLOB datatype. Now when I try to retrieve the data from remote tab1 by joining that view and tab1 ,I am getting the error
ORA-22992: cannot use LOB locators selected from remote tables .
But if I retrieve the data from view alone, I am able to retrieve the information.
And if try to access the varchar2 field alone using dblinks that also will work. But if I combine both the view and same table used in that view, it doesn't work.
I think this can be solved by puting all the required fields(CLOB and non-CLOB) in view. In real situation, the number of fileds that will not have CLOB datatype in tab1 is high.
Can someone tell some suggestion on how to resolve this?
Thanks in Advamce,
Dalia

Answer 1

I assume that you likely do not have Metalink (Oracle Support) access. Here is the Metalink Note on this topic.
Subject:  ORA-22992 When Trying To Select Lob Columns Over A Database Link
Doc ID:   Note:119897.1      
Type:      BULLETIN
Last Revision Date:      24-JUL-2002      
Status:  PUBLISHED
PURPOSE
This document discusses whether or not a lob column can be selected over a
remote database link.
SCOPE & APPLICATION
This document is written for all audiences.
This information is based on the tests made in Oracle 8.1.5 and Oracle 8.1.6
and the available Oracle documentation on LOB (large Object) data and issues
logged with Development on the select of a LOB column over a remote database
link.
How to select a LOB column over a database link?
(A) You cannot actually select a lob column (i.e. CLOB column) from a table
     using remote database link.  This is not a supported feature.
For example,
You run the following command from the local instance to a remote database
instance called R816 over a dblink R816 created in the local instance for user
SCOTT. You have logged in as user Scott and the remote table CLOBT has 2
columns C1 and C2 as below:
$ sqlplus scott/tiger@r816utf8
SQL> create database link r816
      connect to scott identified by tiger
      using 'rtcsol1_r816.us.oracle.com';
SQL> desc clobt@r816
      Name                          NUll?    Type
      C1                            NOT NULL NUMBER
      C2                                     CLOB
  SQL> select c1, c2
       from clobt@R816;
       ORA-22992: cannot use LOB locators selected from remote tables
  SQL> select c1, dbms_lob.getlength(c2)
       from clobt@R816;
       ORA-22992: cannot use LOB locators selected from remote tables
  Error:  ORA-22992
  Text:   cannot use LOB locators selected from remote tables
  Cause:  A remote LOB column cannot be referenced.
  Action: Remove references to LOBs in remote tables.
(B) Also, these are the INVALID operations on a LOB column:
     1. SELECT lobcol from table1@remote_site;
     2. INSERT INTO lobtable select type1.lobattr from table1@remote_site;
     3. SELECT dbms_lob.getlength(lobcol) from table1@remote_site;
In short, you cannot select a lob column using remote dblink. You have to use
DBMS_LOB package in a programming language like PL/SQL, JAVA to manipulate LOB
data.
RELATED DOCUMENTS
Oracle8i Application Developer's Guide - Large Objects (LOBs) Release 2 (8.1.6)
Chapter Managing LOBs: LOB Restrictions