{ account:"abc", vendor:"amazon", } ... { account:"abc", vendor:"overstock", } 想得到 { account:"abc", vendorCount:2 } b.collection.aggregate([ { $group: { _id: { account: '$account' }, vendors: { $addToSet: '$vendor'} } }, { $unwind:"$vendors" }, { $group: { _id: "$_id", vendorCount: { $sum:1} } } ]);
改名重新归类统计
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转载自wang-peng1.iteye.com/blog/1988704
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