我有一个数据库里面大概有 200 万个文档, 数据结构大致如下:
{
"history_id": [1, 2, 3],
"author": "andy",
...
}
如何得到数组的长度并统计当前集合内history_id这个字段有总共有多少个元素?
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2 replies • 2017-09-05 15:01:12 +08:00
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1
way2explore2 Sep 5, 2017  1
Please google and see:
` db.test.insert({username:"Alex", tags: ['C#', 'Java', 'C++'] }); db.test.aggregate( {$match: {username : "Alex"}}, {$unwind: "$tags"}, {$project: {count:{$add:1}}}, {$group: {_id: null, number: {$sum: "$count" }}} ); { "result" : [ { "_id" : null, "number" : 3 } ], "ok" : 1 } ` https://stackoverflow.com/questions/6722850/querying-internal-array-size-in-mongodb#13896341 |
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2
scriptB0y Sep 5, 2017
如何得到数组的长度并统计当前集合内 history_id 这个字段有总共有多少个元素?
这句话我没看懂 |
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