mysql - MYSQL：一个查询以多对多关系复制新项目的分配

Question

您好我的情况是用户被分配到多对多关系的项目中。每次我添加新用户时，我希望为他复制现有的分配，换句话说，将他分配给所有项目，其他用户也被分配。目前我复制整个表，然后按如下方式重新插入，但想知道是否可以在一个查询中排序？

# tmp_assignments already exist and have same fields as assignment
truncate tmp_assignments;
INSERT tmp_assignments SELECT * FROM assignments;
# 38 is new user id
insert into assignments (project,user)
  select a.project,38
  from tmp_assignments as a group by project;

Answer 1

这样做有什么问题：

insert into assignments (project, user) select project, 38 from assignments group by project