Updating a varchar2(1) column

Question

hi,
i need to update load_status_cd, a varchar2(1) column with ' 0 ' based on a condition as below..
Which of the following way is the right choice to use?
UPDATE master_adrs_rate_center_xref a
SET a.load_status_cd =
SELECT 0 FROM master_address b
WHERE
a.mast_pri_address_id = b.mast_pri_address_id
AND a.row_modify_dt < b.last_update_date
UPDATE master_adrs_rate_center_xref a
SET a.load_status_cd = '0'
where exists(
SELECT 1 FROM
master_address b
WHERE
a.mast_pri_address_id = b.mast_pri_address_id
AND a.row_modify_dt < b.last_update_date);

Answer 1

Second is the correct query.
First query will update wrong. It will update 0 for the records where your join condition is met and for the remaining records it will update NULL which will be totally wrong. With the introduction of where clause, your first query would be perfect
UPDATE master_adrs_rate_center_xref a
SET a.load_status_cd =
SELECT 0 FROM master_address b
WHERE
a.mast_pri_address_id = b.mast_pri_address_id
AND a.row_modify_dt < b.last_update_date
where exists
SELECT 0 FROM master_address b
WHERE
a.mast_pri_address_id = b.mast_pri_address_id
AND a.row_modify_dt < b.last_update_date
)