Get your ideas to market faster with a flexible, AI-ready database. MongoDB makes working with data easy.
在之前的文章中,学习了MongoDB中往表里面插入数据的方法,接下来,让我们一起了解一下在MongoDB中查询数据是怎么样去写的: 查询主要是用find()方法:db.getCollection("user").find(query,projection) 参数说明: query:查询条件,非必填 projection:设置返回结果中要返回哪些字段,非必填,默认都返回 下面按照mysql中的...
1) single condition query 、example:: db.getCollection("users").find({"_id": ObjectId('65f1c96179aca875733ae5f1')}); 2)multiple condition query 、example : A、db.getCollection("users").find({$and:[{"age": 20},{"_id": ObjectId('65f3a66a27290000470074b7')}]}) database screens...
In this example,timestampis the name of thetimeFieldandmetadatais the name of themetaField. The value of thetimestampfield must be adatetype. Important Choosing the rightmetaFieldfor your collection optimizes both storage and query performance. For more information onmetaFieldselection and best ...
下面进入javascript代码,其在mongo/shell/collection.js. //这里因为我们只设置了query,所以其它选项都是空的,.DBCollection.prototype.find = function(filter, projection, limit, skip, batchSize, options) { // Verify that API version parameters are not supplied via the shell helper. ...
You cannot use $size to find a range of sizes (for example: arrays with more than 1 element). If you need to query for a range, create an extra size field that you increment when you add elements. 7)$exists $exists用来判断一个元素是否存在: ...
or条件查询:db.inventory.find( { $or: [ { status: "A" }, { qty: { $lt: 30 } } ] } ) and和or的复合条件:db.inventory.find( {status: "A", $or: [ { qty: { $lt: 30 } }, { item: /^p/ } ]}) 查询一条:db.collection.findOne() ...
(If the value of a field returned from a query that iscovered by an indexis NaN, the type of that NaN value isalways double); 3.13multikey index不支持covered query。 4.交叉索引 MongoDB可以使用多个索引的交叉来满足查询,通常每个交叉索引包含两个索引,但是MongoDB能够使用多个或嵌套索引交叉来实现...
MongoDB 查询文档 MongoDB 查询文档使用 find()、findOne() 方法。 find() 方法以非结构化的方式来显示所有文档。 语法 MongoDB 查询数据的语法格式如下: db.collection.find(query, projection) query:用于查找文档的查询条件。默认为 {},即匹配所有文档。projection(
" }planSummary: COLLSCANcursorid:107924518157keysExamined:0 docsExamined:179370numYields:1401 nreturned:179370 reslen:16777323 locks:{ Global: { acquireCount: { r: 1402 } }, Database: { acquireCount: { r: 1402 } }, Collection: { acquireCount: { r: 1402 } } } protocol:op_query 102ms...