Update multiple columns in MERGE statement ORACLE - sql

Question

I want to update multiple columns in MERGE statement,but for each column the conditions are different.How can I achieve it.
I have more than 1 million rows in both the tables.All columns are number.Except Id all 3 columns have number with precision around 18 digits
eg: 1.34255353433230675
Is there a better way to Update.Around 50,000 rows might update daily So I have to merge the updates values to target table.
I tried UPDATE and FORALL but its slow.
I basically want to merge the difference based on common ID column.Any other approach is better?
DECLARE
TYPE test1_t IS TABLE OF test.score%TYPE INDEX BY PLS_INTEGER;
TYPE test2_t IS TABLE OF test.id%TYPE INDEX BY PLS_INTEGER;
TYPE test3_t IS TABLE OF test.Crank%TYPE INDEX BY PLS_INTEGER;
TYPE test4_t IS TABLE OF test.urank%TYPE INDEX BY PLS_INTEGER;
vscore test1_t;
vid test2_t;
vcrank test3_t;
vurank test4_t;
BEGIN
SELECT id,score,crank,urank
BULK COLLECT INTO vid,vscore,vcrank,vurank
FROM test;
FORALL i IN 1 .. vid.COUNT
MERGE INTO final T
USING (SELECT vid (i) AS o_id,
vcrank (i) AS o_crank,
vurank (i) AS o_urank
vscore (i) AS o_score
FROM DUAL) S
ON (S.o_id = T.id)
WHEN MATCHED THEN
UPDATE SET T.crank = S.o_crank
WHERE T.crank <> S.o_crank;
UPDATE SET T.crank = S.o_crank
WHERE T.crank <> S.o_crank;
UPDATE SET T.crank = S.o_crank
WHERE T.crank <> S.o_crank;
UPDATE SET T.score = S.score
WHERE T.score <> S.score;
-- I tried the below case its not working either...
-- UPDATE SET T.crank = (CASE WHEN T.crank <> S.o_crank
-- THEN S.o_crank
-- END),
-- T.urank = (CASE WHEN T.urank <> S.o_urank
-- THEN S.o_urank
-- END);
COMMIT;
END;
/

Answer 1

I don't think you need the loop. I'm assuming your id's are primary keys and you didn't mean to repeat crank several times in your example.
Would something like this work?
Edit per Raj A's comment. This will only update rows where one of the other fields has changed. Note that this will not update rows where one is NULL and the other is not NULL.
MERGE INTO final T
USING ( SELECT id, score, crank, urank FROM test ) S
ON ( S.vid = T.id AND
( S.crank != T.crank OR S.score != T.score OR S.urank != T.urank ))
WHEN MATCHED SET crank = S.crank, score = S.score,
crank = S.crank, urank = S.urank
WHEN NOT MATCHED THEN INSERT
[... not sure what you want to do in this case ...]