Create a key-preserved view across Oracle tables with descending indexes
if you are not required to create view, but just to update using join, then we can use a workaround with a MERGE statement.

merge into TEST_KEY_PRES_A pa 
using TEST_KEY_PRES_B pb
  on (pa.KEY1 = pb.KEY1 and pa.KEY2 = pb.KEY2 and pa.VAL1 &gt; 3 and pa.KEY1 = 'K15')
 when matched then update
   set VAL2 = 'V2-5-X';