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我在这里阅读了它的官方文档:
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.
但是并没有解释什么是“schema support”。为什么 Postgresql 在 Django 上比其他(MySQL 等)更强大?