"distinct" makes use of the the index if its available. Run it like this and see if index is being used: db.runCommand({distinct:"collectionNameGoesHere",key:"fieldNameGoesHere"}) the last value in the returned result set is stats that looks like this: "stats": {...
If the value of the specifiedfieldis an array,distinctconsiders each element of the array as a separate value. For instance, if a field has as its value[ 1, [1], 1 ], thendistinctconsiders1,[1], and1as separate values. Starting in MongoDB 6.0, thedistinctcommand returns the same res...
importpymongo# 连接MongoDB数据库client=pymongo.MongoClient("mongodb://localhost:27017/")database=client["mydatabase"]# 选择集合collection=database["mycollection"]# 执行distinct查询distinct_values=collection.distinct("field_name")# 处理查询结果forvalueindistinct_values:print(value) 1. 2. 3. 4. 5...
Then$groupto get the count for each element. And the re-grouping again but using_idasnullto get all values into one single array. Every element here will be an object withkandvattributes. That will be used in the next stage. Last stage is$projectto not output the_idvalue ...
1. 大于,小于,大于或等于,小于或等于,不等于2. value是否在List中:in 和 not in3. 判断元素是否存在exists4.selectdistinct的实现:5.查询嵌入对象的值6.数组大小匹配size7. 全部匹配 本博客将列举一些常用的MongoDB操作,方便平时使用时快速查询,如find, count, 大于小于不等, select distinct, groupby等 ...
{ "_id" : { "DEPTNO" : 20, "DNAME" : "RESEARCH" }, "value" : { "AVG_SAL_DEPT" : 2258.3333333333335 } } 1. 2. 总体看起来,用mongodb处理结构化数据,还是显得不那么直观,解法也显得很迂回。当然,如果适应了的话,写这些代码可能会变快,但是比起SQL对数据的抽象程度和友好性来说,mongodb还是...
在MongoDB中,$group操作符可以对集合中的文档进行分组,并对每个组执行聚合操作,它的基本语法如下: { $group: { _id: <expression>, // 用于分组的表达式 : { <accumulator1> : <value1> }, // 输出字段1及其累加器 ... : { <accumulatorN> : <valueN> } // 输出字段N及其累加器 } } <expressi...
New in version 1.5. Return Values An array of the distinct values. Errors/Exceptions MongoDB\Exception\UnexpectedValueExceptionif the command response from the server was malformed. MongoDB\Exception\UnsupportedExceptionif options are used and not supported by the selected server (e.g.collation,read...
Explanation:In the above example, we have retrieved distinct values from the grades field. The above example states that distinct methods in MongoDB consider the array field as each element of the field as a separate value. In the above example output of 92 and 95 occur double because distinc...
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