为什么Google App Engine会限制GQL查询？

问题描述

我在wikipedia上阅读了，并且遇到了一些GQL限制：

• JOIN不受支持




• table




• 最多可以在WHERE子句中放置1列

这些限制的优点是什么？

这些限制在可伸缩性优先的其他地方常见吗？

解决方案

GQL与之交谈的数据存储是： 不是像MySQL或PostgreSQL这样的关系型数据库

是一个名为BigTable的面向列的DBMS

像这样的数据库的一个原因是有一个非常高的性能数据库，您可以扩展到数百个服务器。

GQL不是SQL，它像SQL一样。

以下是一些参考资料：

I was reading about App Engine on wikipedia and came across some GQL restrictions:

• JOIN is not supported

• can SELECT from at most one table at a time

• can put at most 1 column in the WHERE clause

What are the advantages of these restrictions?

Are these restrictions common in other places where scalability is a priority?

解决方案

The datastore that GQL talks to is:

• not a relational database like MySQL or PostgreSQL
• is a Column-oriented DBMS called BigTable

One reason to have a database like this is to have a very high performance database that you can scale across hundreds of servers.

GQL is not SQL it is SQL-like.

Here are some references:

• http://en.wikipedia.org/wiki/Column-oriented_DBMS
• http://en.wikipedia.org/wiki/BigTable
• http://code.google.com/appengine/docs/datastore/overview.html
• http://code.google.com/appengine/docs/datastore/gqlreference.html

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