如何在mongodb中查找最小值 [英] How to find min value in mongodb

问题描述

您如何做等同于

SELECT 
  MIN(Id) AS MinId
FROM
  Table

使用MongoDB吗?

with MongoDB?

看起来我将不得不使用MapReduce，但是我找不到任何显示该操作方法的示例.

It looks like I will have to use MapReduce but I can't find any example that shows how to do this.

推荐答案

您可以使用sort和limit的组合来模拟min:

You can use a combination of sort and limit to emulate min:

> db.foo.insert({a: 1})
> db.foo.insert({a: 2})
> db.foo.insert({a: 3})
> db.foo.find().sort({a: 1}).limit(1) 
{ "_id" : ObjectId("4df8d4a5957c623adae2ab7e"), "a" : 1 }

sort({a: 1})是对a字段的升序(最小优先)排序，然后我们仅返回第一个文档，该文档将是该字段的最小值.

sort({a: 1}) is an ascending (minimum-first) sort on the a field, and we then only return the first document, which will be the minimum value for that field.

编辑:请注意，这是用mongo shell编写的，但是您可以使用适当的驱动程序方法从C#或任何其他语言中执行相同的操作.

note that this is written in the mongo shell, but you can do the same thing from C# or any other language using the appropriate driver methods.

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