标签：null 取出 line char key hang _id beijing 子查询
create table student
( student_id int not null ,student_name varchar(30) not null ,city_code varchar(10) null ,city_name varchar(50) null);create table city( code varchar(10) not null ,name varchar(50) not null);insert into student values(1, ‘john‘, ‘001‘, null);insert into student values(2, ‘nick‘, ‘002‘, null);insert into city values(‘001‘, ‘beijing‘);insert into city values(‘002‘, ‘shanghai‘);insert into city values(‘003‘, ‘shenzhen‘);有两个表：student & city，现在需要取出 city.name 来更新 student.city_name。两表关联条件是 student.city_code=city.code。update student s, city c set s.city_name = c.name where s.city_code = c.code;也可以试下面的相关子查询：update student s set city_name = (select name from city where code = s.city_code);标签：null 取出 line char key hang _id beijing 子查询
原文地址：https://www.cnblogs.com/moris5013/p/10670425.html
