ORA-00932: inconsistent datatypes: expected - got CLOB

Take a substr of the CLOB and then convert it to a char:

UPDATE IMS_TEST 
  SET TEST_Category           = 'just testing' 
WHERE to_char(substr(TEST_SCRIPT, 1, 9))    = 'something'
  AND ID                      = '10000239';

I just ran over this one and I found by accident that CLOBs can be used in a like query:

   UPDATE IMS_TEST 
   SET TEST_Category  = 'just testing'  
 WHERE TEST_SCRIPT    LIKE '%something%'
   AND ID             = '10000239' 

This worked also for CLOBs greater than 4K

The Performance won't be great but that was no problem in my case.

The same error occurs also when doing SELECT DISTINCT ..., <CLOB_column>, ....

If this CLOB column contains values shorter than limit for VARCHAR2 in all the applicable rows you may use to_char(<CLOB_column>) or concatenate results of multiple calls to DBMS_LOB.SUBSTR(<CLOB_column>, ...).

You can't put a CLOB in the WHERE clause. From the documentation:

Large objects (LOBs) are not supported in comparison conditions. However, you can use PL/SQL programs for comparisons on CLOB data.

If your values are always less than 4k, you can use:

UPDATE IMS_TEST 
   SET TEST_Category           = 'just testing'  
 WHERE to_char(TEST_SCRIPT)    = 'something'
   AND ID                      = '10000239';

It is strange to search by a CLOB anyways.. could you not just search by the ID column?