Multiple columns and rows update using select staement

Question

i am trying to update the 2 colums of a table based on the cursor result set with key values are matching.
DECLARE
CURSOR update_master
IS
SELECT B.cust_num,c.cust_num,
B.cust_name,B.cust_bal
FROM
Table_one B
JOIN
Table_two C
ON B.cust_num= C.cust_num;
BEGIN
FOR master_rec IN update_master
LOOP
UPDATE Table_three
SET col1 = master_rec.cust_name,
Col2 = master_rec.cust_bal,
Where WHERE Cust_num = master.cust_num;
END LOOP;
COMMIT;
END;
The 3 tables are having around 50000 records individually............
It is taking too much of time to execute......more than 6 minutes......
how can we optimize it?? can we write this update statement directly? instead of writing it in procedure?

Answer 1

Here's a general approach:
update some_table s
set   (s.col1, s.col2) = (select x.col1, x.col2
                          from   other_table x
                          where  x.key_value = s.key_value
where exists             (select 1
                          from   other_table x
                          where  x.key_value = s.key_value
;