mongodb的aggregate學習之1-pipeline

想知道某個country和province下userid的數量，相同userid算一個

如果這麼寫，      

[      

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

]
      

傳回了      

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

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

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

}
      

從結果來看，計算結果是按照country和province分組了，就是同一個country和province下有幾條資料，      

不是我們想要的結果，再改      

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

傳回了      

{"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}
			}
	}
];
      

傳回了      

{"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}      

]}
      

和上一個的結果相比，就是count都變成了1，還不是想要的結果，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}
			}
	}
];
      

就是注釋了一點點的代碼，傳回結果      

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

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

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

是想要的結果了