先来几个简单的示例
solution 1:  1列
update student s, city c set s.city_name = c.name where s.city_code = c.code;
solution 2: 多个列
update a, b set a.title=b.title, a.name=b.namewhere a.id=b.id
solution 3: 子查询
update student s set city_name = (select name from city where code = s.city_code);
我们再来看几个负责写的
例如: 把表 tk_zyt_scenery_order的 字段更新到 t_advs_order中去, 一般可能会这样写:
update t_advs_order set attribute1=(select o.order_state from tk_zyt_scenery_order o where o.order_id=`on`), attribute2=(select o.order_state from tk_zyt_scenery_order o where o.order_id=`on`) where exists (select o.order_state from tk_zyt_scenery_order o where o.order_id=`on`);
这样效率比较低下, 优化写法:
update t_advs_order a inner join tk_zyt_scenery_order s on s.order_id=a.`on` set a.attribute1=s.order_id, a.attribute2=s.order_id;