Strange behaviour of optimizer

I have the following tables:

MAIN(docnum number(10) primary key, heading varchar2(4)...) TEXT(docnum number(10) primary key, inhalt varchar2(4000))

"heading" is normally index, "inhalt" is indexed with a context.ctxsys index.

Searches like
  select docnum from MAIN where heading='...'   select docnum from TEXT where contains(inhalt,'...')>0;

work fine and fast. However the following query take minutes:

select docnum from MAIN where heading='...' or docnum IN ( select docnum from TEXT where contains(inhalt,'any text')>0);

I am using Oracle 8k and the CBO (all tables and indexes are analyzed). Any idea why this happens ?

Andreas

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   Andreas Jung, Saarbr|cker Zeitung Verlag und Druckerei GmbH
   Saarbr|cker Daten-Innovations-Center
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