Data Cleaning of Two Tables in MYSQL

  node.js, question

Both tables have two identical fields, for example, table a has cityId,cityName.B also has cityId,cityName.
CityId and cityName in table b have values. Table A has a large amount of data, cityId has values and all values are contained in Table A. CityName is empty. How to fill cityName of table a according to table b?

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