1、单表更新
update customers
set city_name='山西省太原市'
where city_name='山西太原'
2、两表(多表)关联update -- 被修改值由另一个表运算而来
update customers a
set city_name=(select b.city_name from tmp_cust_city b where b.customer_id=a.customer_id)
where exists (select 1
from tmp_cust_city b
where b.customer_id=a.customer_id)
-----------------------------------------------------------------Take more responsibility！---------------------------------------------------------
