orcale update join

UPDATE WATCHER_TASK a 
SET a.LAST_MODIFIER_ID = (
    SELECT
        b.USER_ID 
    FROM
        task_user b 
    WHERE
        a.TASK_ID = b.TASK_ID 
        AND b.TASK_TYPE = 3 
        AND b.USER_IDENTITY = 1 
        AND b.DEL_FLAG = 0 
    ) 
WHERE
    a.DEL_FLAG = 0