How optimizing my query ?

Hi,

The following query takes a very long time :
UPDATE /*+parallel (LHMS.CYCLE_TEMPO,3) */ LHMS.CYCLE_TEMPO
SET ENGINEPOSITION = (SELECT distinct ea.POSITION FROM ENGINEATTRIBUTION ea , CYCLE c
WHERE CYCLE_TEMPO.ENGINE_ID = ea.ENGINE_ID
AND CYCLE_TEMPO.CYCLE_ID = c.CYCLE_ID
AND c.PLANE_ID = ea.PLANE_ID)
WHERE EXISTS
(SELECT null FROM ENGINEATTRIBUTION ea , CYCLE c
WHERE CYCLE_TEMPO.ENGINE_ID = ea.ENGINE_ID
AND CYCLE_TEMPO.CYCLE_ID = c.CYCLE_ID
AND c.PLANE_ID = ea.PLANE_ID) ;


I've killed the query after 24 hours.

I tried another query without the distinct, but it's always very long :