Updating large table using the WITH CLAUSE or PLSQL

Question

I tried to perform an update on a table with over 15million records using the merge statement below but it's very slow.
Can someone help me re-writting this statement using the WITH CLAUSE or a PLSQL statement that will make it run faster?
my merge statemet:
MERGE INTO voter dst
USING (
SELECT voterid,
pollingstation || CASE
WHEN ROW_NUMBER () OVER ( PARTITION BY pollingstation
ORDER BY surname, firstnames
) <= 1000
THEN 'A'
WHEN ROW_NUMBER () OVER ( PARTITION BY pollingstation
ORDER BY surname, firstnames
) BETWEEN 1000 AND 2000
THEN 'B'
ELSE 'C'
END AS new_pollingstation
FROM voter
) src
ON (src.voterid = dst.voterid)
WHEN MATCHED THEN UPDATE
SET dst.new_pollingstation = src.new_pollingstation
the with clause approach:http://www.dba-oracle.com/t_with_clause.htm
thanks.

Answer 1

Well, here's your query formatted for people to read...
MERGE INTO voter dst
USING (SELECT voterid,
              pollingstation || CASE WHEN ROW_NUMBER () OVER ( PARTITION BY pollingstation ORDER BY surname, firstnames) <= 1000
                                       THEN 'A'
                                     WHEN ROW_NUMBER () OVER ( PARTITION BY pollingstation ORDER BY surname, firstnames) BETWEEN 1000 AND 2000
                                       THEN 'B'
                                     ELSE 'C'
                                END AS new_pollingstation
       FROM voter) src
ON (src.voterid = dst.voterid)
WHEN MATCHED THEN
UPDATE SET dst.new_pollingstation = src.new_pollingstation
;In future, please read {message:id=9360002} and post relevant details.
What do you mean when you say it's "slow"? How have you measured this? Have you examined the explain plan?
Take a read of the threads linked to by the FAQ post: {message:id=9360003} for details of what you need to provide to get help with performance issues.