Update a column (please its urgent)

Question

I am trying to update a column while the command updates that specific column and replace the rest with blank.
i have written this command
UPDATE AU_POI_INTERM A SET (A. PREV_REL_IDX)= (SELECT REL13_IDX FROM TEMP_AU_POI_DUPLICATES B
WHERE B.REL13_SID='10143' AND B.NEW_IDX = A.IDX)
this is the maximum criteria i can use in where clause.

Answer 1

It updated every row because you have no WHERE clause (on your update statement). Try this:
UPDATE AU_POI_INTERM A
SET   (A. PREV_REL_IDX) = (SELECT REL13_IDX
                           FROM   TEMP_AU_POI_DUPLICATES B
                           WHERE  B.REL13_SID='10143'
                           AND    B.NEW_IDX = A.IDX)
WHERE EXISTS              (SELECT REL13_IDX
                           FROM   TEMP_AU_POI_DUPLICATES B
                           WHERE  B.REL13_SID='10143'
                           AND    B.NEW_IDX = A.IDX)
;