MongoDB 选择计数组

本文介绍了MongoDB 选择计数组的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我正在玩 MongoDB，试图弄清楚如何做一个简单的

I am playing around with MongoDB trying to figure out how to do a simple

SELECT province, COUNT(*) FROM contest GROUP BY province

但我似乎无法使用聚合函数来计算它.我可以使用一些非常奇怪的组语法来做到这一点

But I can't seem to figure it out using the aggregate function. I can do it using some really weird group syntax

db.user.group({ "key": { "province": true }, "initial": { "count": 0 }, "reduce": function(obj, prev) { if (true != null) if (true instanceof Array) prev.count += true.length; else prev.count++; } });

但是使用聚合函数有更简单/更快的方法吗?

But is there an easier/faster way using the aggregate function?

推荐答案

这将是使用 聚合:

This would be the easier way to do it using aggregate:

db.contest.aggregate([ {"$group" : {_id:"$province", count:{$sum:1}}} ])