MongoDB SELECT COUNT GROUP BY [英] MongoDB SELECT COUNT GROUP BY

问题描述

我正在玩弄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计算出来。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 aggregate ：

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

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

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