mongodb的aggregate学习之1-pipeline

最新推荐文章于 2025-02-12 15:04:35 发布

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最新推荐文章于 2025-02-12 15:04:35 发布

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文章标签： mongodb pipeline aggregate 分组 group

本文链接：https://blog.youkuaiyun.com/zgrbsbf/article/details/78422586

本文通过逐步调整MongoDB聚合管道的查询方式，最终实现了按国家和省份统计唯一userid数量的目标。过程中展示了不同分组方式对统计结果的影响。

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想知道某个country和province下userid的数量，相同userid算一个

如果这么写，

{
		$group:
			{
				"_id": {"country": "$country", "province": "$province"},
				'count': {$sum: 1}
			}
	}

返回了

{"result":[{"_id":{"country":"us","province":"shandong"},"count":2},

	{"_id":{"country":"cha","province":"beij"},"count":1},

	{"_id":{"country":"cha","province":"shandong"},"count":3}]

从结果来看，计算结果是按照country和province分组了，就是同一个country和province下有几条数据，

不是我们想要的结果，再改

[{
		$group:
			{
				"_id": {"country": "$country", "province": "$province", "uid": "$userid"},
				'count': {$sum: 1}
			}
	}]

返回了

{"result":[{"_id":{"country":"cha","province":"beij","uid":"aaa"},"count":1},

          {"_id":{"country":"us","province":"shandong","uid":"aaa"},"count":2},

          {"_id":{"country":"cha","province":"shandong","uid":"bbb"},"count":2},

          {"_id":{"country":"cha","province":"shandong","uid":"aaa"},"count":1}

]}

再改，

[
	{
		$group:
			{
				"_id": {"country": "$country", "province": "$province", "uid": "$userid"},
				'count': {$sum: 1}
			}
	},
	{
		$group:
			{
				"_id": {"country": "$_id.country", "province": "$_id.province", "uid": "$_id.uid"},
				'count': {$sum: 1}
			}
	}
];

返回了

{"result":[{"_id":{"country":"cha","province":"shandong","uid":"aaa"},"count":1},

         {"_id":{"country":"cha","province":"shandong","uid":"bbb"},"count":1},

         {"_id":{"country":"us","province":"shandong","uid":"aaa"},"count":1},

          {"_id":{"country":"cha","province":"beij","uid":"aaa"},"count":1}

]}

和上一个的结果相比，就是count都变成了1，还不是想要的结果，再改改

[
	{
		$group:
			{
				"_id": {"country": "$country", "province": "$province", "uid": "$userid"},
				'count': {$sum: 1}
			}
	},
	{
		$group:
			{
				"_id": {"country": "$_id.country", "province": "$_id.province", /*"uid": "$_id.uid"*/},
				'count': {$sum: 1}
			}
	}
];

就是注释了一点点的代码，返回结果

{"result":[{"_id":{"country":"us","province":"shandong"},"count":1},

         {"_id":{"country":"cha","province":"shandong"},"count":2},

          {"_id":{"country":"cha","province":"beij"},"count":1}]}

是想要的结果了