問題描述

問題解答

create table tb1( country int, province int, city int);create table tb2( country int, province int, city int);insert into tb1 (country, province, city) values (1, 2, 5), (1, 3, null);insert into tb2 (country, province, city) values (1, 2, 5), (1, 3, 7);select * from tb1;select * from tb2;update tb1inner join tb2 on tb1.country=tb2.country and tb1.province=tb2.provinceset tb1.city=tb2.citywhere tb1.city is null; -- and tb1.xx=?select * from tb1;select * from tb2;

update from 語句在 mssql 中有效, mysql 似乎無法正常執行

update tb1 set city=r.city from (select country, province, city from tb2) as rwhere tb1.city is null and tb1.country=r.country and tb1.province=r.province

http://sqlfiddle.com/#!9/4df7d7/2