MySQL 从一张表update字段到另外一张表中，mysqlup

MySQL 从一张表update字段到另外一张表中，mysqlupdate

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.name
where 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;