如何使用MySQL一个表中的字段更新另一个表中字段

update student s, city c
set s.city_name = c.name
where s.city_code = c.code;

update a, b
set a. =b. , a.name=b.name
where a.id=b.id

update student s set city_name = (select name from city where code = s.city_code);

UPDATE \"SYS_ROLE\" A
SET A .\"DEPT_ID\" = (
  SELECT
    c.\"id\"
  FROM
    \"his_department_info\" c
  WHERE
    c.\"dept_name\" = A .\"ROLE_NAME\"