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mongodb 怎么對類型為list的字段的值進(jìn)行匯總統(tǒng)計(jì)

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慕哥6287543 2019-05-25 15:06:11

mongodb中有一個字段為list類型如下，tags想要對tags內(nèi)的'a、b、c、d'其進(jìn)行計(jì)數(shù)統(tǒng)計(jì){'_id':ObjectId('594e473dd746002ad0464b36'),'tags':['a','b','d']}{'_id':ObjectId('59637962d7460028c05590ef'),'tags':['a','c','d']}{'_id':ObjectId('59637962d7460028c0558ff6'),'tags':['c','d']}統(tǒng)計(jì)tags內(nèi)的'a','b','c','d'每個都出現(xiàn)了幾次。期待的結(jié)果[{'name':'a','count':2},{'name':'b','count':1},{'name':'c','count':2},{'name':'d','count':3}]該怎么寫這個查詢語句呢？

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2 回答

哆啦的時光機(jī)

TA貢獻(xiàn)1779條經(jīng)驗(yàn) 獲得超6個贊

數(shù)據(jù)源db.getCollection('test').insert([{'tags':['a','b','d']},{'tags':['a','d']},{'tags':['b','d']}])SQLdb.getCollection('test').aggregate([{$unwind:'$tags'},{$group:{_id:'$tags',count:{$sum:1}}}])結(jié)果/*1*/{"_id":"d","count":3.0}/*2*/{"_id":"b","count":2.0}/*3*/{"_id":"a","count":2.0}如果你要將查詢結(jié)果的_id字段名改為name,那么就要再加個$projectdb.getCollection('test').aggregate([{$unwind:'$tags'},{$group:{_id:'$tags',count:{$sum:1}}},{$project:{_id:0,name:'$_id',count:'$count'}}])

反對回復(fù) 2019-05-25

翻翻過去那場雪

TA貢獻(xiàn)2065條經(jīng)驗(yàn) 獲得超14個贊

db.collection.aggregate([{$unwind:"$tags"},{$group:{_id:"$tags",count:{$sum:1}}},{$project:{name:"$_id",count:"$count",_id:0}}]);$unwind,$group,$project都是很常用的運(yùn)算符，先查下文檔看咯，不懂再說。

反對回復(fù) 2019-05-25