node.js - MYSQL 中两个表的数据清洗问题

Question

两个表分别都有两个相同的字段比如A表有cityId,cityName.B表也有cityId,cityName.
B表的cityId和cityName都有值。A表有大量数据cityId有值且值都包含在A表。cityName为空。如何去根据B表填充A表的cityName?

Answer 1

update A join B set A.cityName=B.cityName on A.cityId=B.cityId

Answer 2

sqlUPDATE  a,  b SET a.cityName = b.cityName  WHERE a.cityId= b.cityId