对于带有字段 { wins: Number } 的某些集合,我如何使用 MongoDB 聚合框架 来获取集合中所有文档的获胜总数?
For some collection with a field { wins: Number }, how could I use MongoDB Aggregation Framework to get the total number of wins across all documents in a collection?
如果我有 3 个文档分别具有 wins: 5、wins: 8、wins: 12,我该如何使用 MongoDB 聚合框架返回总数,即total: 25.
If I have 3 documents with wins: 5, wins: 8, wins: 12 respectively, how could I use MongoDB Aggregation Framework to return the total number, i.e. total: 25.
推荐答案Sum
使用 MongoDB 的聚合框架时,要获取分组字段的总和,您需要使用 $group 和 $sum:
db.characters.aggregate([ { $group: { _id: null, total: { $sum: "$wins" } } } ] )在这种情况下,如果要获取所有wins的总和,则需要使用$语法将字段名称引用为$wins 它只是从分组的文档中获取 wins 字段的值并将它们汇总在一起.
In this case, if you want to get the sum of all of the wins, you need to refer to the field name using the $ syntax as $wins which just fetches the values of the wins field from the grouped documents and sums them together.
您也可以通过传入特定值来sum 其他值(正如您在评论中所做的那样).如果你有
You can sum other values as well by passing in a specific value (as you'd done in your comment). If you had
{ "$sum" : 1 },
这实际上是所有 wins 的计数,而不是总数.
that would actually be a count of all of the wins, rather than a total.
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如何在 MongoDB 中汇总总和以获得总计数?
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