迁移到MongoDB:如何查询GROUP BY + WHERE [英] Migrating to MongoDB: how to query GROUP BY + WHERE

问题描述

我有一个MYSQL表，上面记录着人们的姓名，到达时间用数字表示.认为这是一场马拉松比赛.我想知道有多少人在某个时间间隔内到达了相同的名字，所以:

I have a MYSQL table with records of people's names and the time of arrival expresed as a number. Think of it as a marathon. I want to know how many people arrived into a certain gap of time who where named the same, so:

SELECT name, COUNT(*) FROM mydb.mytable
WHERE Time>=100 AND Time<=1000
GROUP BY name

结果我得到了:

Susan, 1
John, 4
Frederick, 1
Paul, 2

我现在正在迁移到MongoDB，并使用Python进行编码(因此，我需要Pymongo帮助).我尝试查找有关GROUP BY的信息(即使我已经读到NoSQL数据库在这种操作上比SQL还要差)，但是由于它们发布了新的Agreggate API，所以我一直无法找到这样的简单示例可以通过group方法，Map-Reduce方法或全新的agreggate API解决.

I'm migrating to MongoDB now, and using Python to code (so I'm asking for Pymongo help). I tried looking for information about the GROUP BY equivalent (even when I have read that NoSQL databases are worse at this kind of operation than the SQL ones), but since they released the new agreggate API, I hjaven't been able to find a simple example like this solved with the group method, the Map-Reduce method or the brand new agreggate API.

有帮助吗?

推荐答案

在文档，Google和此网站上都有一些示例.

There are examples of this all over the documentation, Google and this site.

一些参考文献:

• http://api.mongodb.org/python/current/examples/Aggregation.html
• http://docs.mongodb.org/manual/reference/aggregation/group /
• http://docs.mongodb.org/manual/reference/aggregation/sum /

• http://api.mongodb.org/python/current/examples/aggregation.html
• http://docs.mongodb.org/manual/reference/aggregation/group/
• http://docs.mongodb.org/manual/reference/aggregation/sum/

对于某些代码:

self.db.aggregate(
    # Lets find our records
    {"$match":{"Time":{"$gte":100,"$lte":1000}}}, 

    # Now lets group on the name counting how many grouped documents we have
    {"$group":{"_id":"$name", "sum":{"$sum":1}}} 
)

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