"namespace":"mldn.students","indexFilterSet":false,"parsedQuery":{"age":{"$eq":19}},"winningPlan":{"stage":"FETCH","inputStage":{"stage":"IXSCAN","keyPattern":{"age":-1},"indexName":"age_-1","isMultiKey":false,"multiKeyPaths":{"age":[]},"isUnique":false,"isSparse":fal...
"Length" : "4:15" } ] } ] > db.mediaCollection.find( { Cast : {$size : 1} } ).toArray() [ ] > db.mediaCollection.find( { Cast : {$size : 6} } ).toArray() [ { "_id" : ObjectId("53548225d85b463e729a2e57"), "Type" : "DVD", "Title" : "Matrix, The", "Rel...
db.qtfm__audio_info.find({playLength:{$gt:2}}) 小于($lt):Less than,值类型需要为int、double... db.qtfm__audio_info.find({playLength:{$lt:2}}) 大于等于($gte):Greater than equals db.qtfm__audio_info.find({playLength:{$gte:2}}) 不等于($ne):Not equals db.qtfm__audio_info.f...
下面的语句就可以匹配:db.things.find( { a : { $size: 1 } } ); 官网上说不能用来匹配一个范围内的元素,如果想找$size<5之类的,他们建议创建一个字段来保存元素的数量。 You cannot use $size to find a range of sizes (for example: arrays with more than 1 element). If you need to query...
MongoDB 如何优化MongoDB性能? MongoDB据说性能不错,但是我的试验确证实在一亿行的数据情况下他和mysql的性能很接近,略有优势,但是没多大优势。 具体测试情况: 在mongo…显示全部 关注者89 被浏览93,617 关注问题写回答 邀请回答 好问题 1 1 条评论 分享 ...
$arrayElemAt会根据第二个参数从数组中选择特定元素。在本例中,1值会从$split运算符生成的数组中选择第二个元素,因为数组索引会从0开始。例如,传递给此操作的值 ["Store", "42"] 将返回值“42”。 constresult =awaitplants.aggregate([ { $project: { ...
"<array>.<index>" 1. 例如存在以下文档: AI检测代码解析 { ... contribs: [ "Turing machine", "Turing test", "Turingery" ], ... } 1. 2. 3. 4. 5. 访问contribs数组第三个元素"Turingery"的表达式为: "contribs.2"。 For examples querying arrays, see: ...
51. 52. 53. 54. 55. 56. 57. 58. 59. 60. 61. 62. 63. 64. 65. 66. 67. 68. 15. $type 根据BSON类型来检索集合中匹配的结果。 MongoDB中可以使用的类型如下表所示: 类型描述 类型值 Double 1 String 2 Object 3 Array 4 Binary data 5 Object id 7 Boolean 8 Date 9 Null 10 Regular...
Calling aggregate without an array of operations or $operations will make it a match. // matches every documentdb.collection.aggregate() db.collection.aggregate({})// matches documents where the "a" is equal to 1db.collection.aggregate({a: 1})// matches documents where "a" is greater tha...
grades: [30, 20, 10] # sum of this array = 60 (don't take this) } 我对该系列进行了如下投影: db.collections.find({}, { { sumOfGrades: { $sum: "$grades" } }) // returns {...sumOfGrades: 170}, {...sumOfGrades: 60} ...