CATSEARCH only works with AND not with Or

Question

Hello,
If I run the following query against my database it runs absolutely fine
SELECT * FROM
LOAD
WHERE ((catsearch (WILDCARD_SURNAMES, 'BRUCE', '') > 0)) AND PARSED_FORENAME1='ANTHONY'
But if I replace the "AND" with an "OR"
SELECT * FROM
LOAD
WHERE ((catsearch (WILDCARD_SURNAMES, 'BRUCE', '') > 0)) OR PARSED_FORENAME1='ANTHONY'
I get an Oracle error
ORA-20000: Oracle Text error:
DRG-10849: catsearch does not support functional invocation
DRG-10599: column is not indexed
I don't understand this, why can't I use OR?
Thanks for any help
Mark

Answer 1

The optimizer has chosen to drive the query from an index on parsed_forename1 or by doing a full table scan.
This causes it to try to invoke the ctxcat index in "functional lookup" mode - effectively saying "does rowid XXX match have the word "BRUCE" in WILDCARD_SURNAMES?"
However, CTXCAT indexes do not support functional lookups, so this is impossible.
The solution is to use a hint which persuades the optimizer to always drive the query from the CTXCAT index.
I know this is kind of messy, but our developers tell me there is no simple way to tell the optimizer that such as call is impossible (or infinitely expensive).