oracle更新大量数据太慢，可以通过游标实现的例子

declare cursor city_cur is
select t.new_customer_id,t.old_customer_id from
citsonline.crm_customer_tmp6 t
where t.new_customer_id!=t.old_customer_id
order by new_customer_id;
begin
for my_cur in city_cur loop

update platform.crm_service_customer_bak s
set s.customer_id=my_cur.new_customer_id
where s.customer_id=my_cur.old_customer_id;

/** 此处也可以单条/分批次提交，避免锁表情况 **/
if mod(city_cur%rowcount,1000)=0 then
dbms_output.put_line('----');
commit;
end if;
end loop;
commit;
end;