mysql 一张表update另一张表

有三种方法：

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);