Getting an error while selecting from table having CLOB column.

Question

Hi All,
I have below table created in My oracle database version Oracle Database 11g Enterprise Edition Release 11.2.0.1.0.
CREATE TABLE my_clob -- Dummy table created
(DataBody CLOB);
Current Database Character set - WE8MSWIN1250.
On the front end of my application, I have one form through which I can save/edit data in the above table. If I'm creating one new entry in the above table then it first check with existing record to avoid the duplicate entry and the this point application create the below select statement on the above table and return the error "ORA-00932: inconsistent data types: expected - got CLOB".
I can not change the sql statement.
SELECT * FROM my_clob WHERE databody IS NULL OR databody ='';
Even when I run the same statement on my DB server I’m getting the same error. Shown below
SQL> SELECT * FROM my_clob WHERE databody IS NULL OR databody ='';
SELECT * FROM my_clob WHERE databody IS NULL OR databody =''
ERROR at line 1:
ORA-00932: inconsistent datatypes: expected - got CLOB
SQL>
Is there anything with OraOLEDB which causing this error? Please help me out to get rid of this error.
Thanks,
Santosh

Answer 1

You cannot compare directly a CLOB column with a VARCHAR2 column. In your case you don't need to do such comparison because Oracle consider zero length strings as null values:
SQL> create table my_clob(data int, databody clob);
Table created.
SQL> insert into my_clob values(1, null);
1 row created.
SQL> insert into my_clob values(2, '');
1 row created.
SQL> commit;
Commit complete.
SQL> select * from my_clob where databody is null;
      DATA
DATABODY
         1
         2About null values in Oracle, please read http://docs.oracle.com/cd/E11882_01/server.112/e26088/sql_elements005.htm#SQLRF30037.