clob 컬럼에 case when이나 is null을 쓴다고 해서 오류가 발생하진 않는 것 같습니다.
버전차이거나 다른 문제일듯 하네요.
iSQL> desc tmp;
[ TABLESPACE : SYS_TBS_MEM_DATA ]
[ ATTRIBUTE ]
------------------------------------------------------------------------------
NAME TYPE IS NULL
------------------------------------------------------------------------------
A CLOB LOB
TMP has no index
TMP has no primary key
iSQL> select case when a like 'a%' then 1 else 0 end from tmp;
CASEWHENALIKE'A%'THEN1ELSE0END
---------------------------------
1
1 row selected.
iSQL> select case when a is null then 1 else 0 end from tmp;
CASEWHENAISNULLTHEN1ELSE0END
-------------------------------
0
1 row selected.
iSQL> select * from tmp where a is null;
A
-----------------------------------------------------------------------------------
No rows selected.