我在这里读到了它的官方文件：

https://docs.djangoproject.com/en/1.8/topics/migrations/

PostgreSQL

PostgreSQL is the most capable of all the databases here in terms of
schema support; the only caveat is that adding columns with default
values will cause a full rewrite of the table, for a time proportional
to its size.

For this reason, it’s recommended you always create new columns with
null=True, as this way they will be added immediately.

但它没有解释什么是"架构支持"。 为什么Postgresql比Django上的其他(MySQL等)更强大？

此引用来自迁移文档。 它指的是PostgreSQL是Django中唯一支持事务DDL的数据库后端。 那就是Postgres可以回滚CREATE TABLE或ALTER TABLE语句，而MySQL，Oracle和SQLite则不能。