在 MongoDB 中获取不同的记录值?
您可以在 MongoDB 中使用 distinct() 方法来获取不同的记录值。语法如下 -
db.yourCollectionName.distinct(“yourFieldName”);
为了理解上述语法,让我们创建一个带有文档的集合。创建带有文档的集合的查询如下 -
> db.distinctRecordDemo.insertOne({"StudentId":1,"StudentName":"John","StudentAge":21}); { "acknowledged" : true, "insertedId" : ObjectId("5c77a78299b97a65744c1b50") } > db.distinctRecordDemo.insertOne({"StudentId":2,"StudentName":"John","StudentAge":22}); { "acknowledged" : true, "insertedId" : ObjectId("5c77a78b99b97a65744c1b51") } > db.distinctRecordDemo.insertOne({"StudentId":3,"StudentName":"Carol","StudentAge":21}); { "acknowledged" : true, "insertedId" : ObjectId("5c77a79a99b97a65744c1b52") } > db.distinctRecordDemo.insertOne({"StudentId":4,"StudentName":"Carol","StudentAge":26}); { "acknowledged" : true, "insertedId" : ObjectId("5c77a7a499b97a65744c1b53") } > db.distinctRecordDemo.insertOne({"StudentId":5,"StudentName":"Sam","StudentAge":24}); { "acknowledged" : true, "insertedId" : ObjectId("5c77a7b499b97a65744c1b54") } > db.distinctRecordDemo.insertOne({"StudentId":6,"StudentName":"Mike","StudentAge":27}); { "acknowledged" : true, "insertedId" : ObjectId("5c77a7c799b97a65744c1b55") } > db.distinctRecordDemo.insertOne({"StudentId":7,"StudentName":"Sam","StudentAge":28}); { "acknowledged" : true, "insertedId" : ObjectId("5c77a7d399b97a65744c1b56") }
在集合中显示所有文档,借助 find() 方法。查询如下 -
> db.distinctRecordDemo.find().pretty();
以下为输出
{ "_id" : ObjectId("5c77a78299b97a65744c1b50"), "StudentId" : 1, "StudentName" : "John", "StudentAge" : 21 } { "_id" : ObjectId("5c77a78b99b97a65744c1b51"), "StudentId" : 2, "StudentName" : "John", "StudentAge" : 22 } { "_id" : ObjectId("5c77a79a99b97a65744c1b52"), "StudentId" : 3, "StudentName" : "Carol", "StudentAge" : 21 } { "_id" : ObjectId("5c77a7a499b97a65744c1b53"), "StudentId" : 4, "StudentName" : "Carol", "StudentAge" : 26 } { "_id" : ObjectId("5c77a7b499b97a65744c1b54"), "StudentId" : 5, "StudentName" : "Sam", "StudentAge" : 24 } { "_id" : ObjectId("5c77a7c799b97a65744c1b55"), "StudentId" : 6, "StudentName" : "Mike", "StudentAge" : 27 } { "_id" : ObjectId("5c77a7d399b97a65744c1b56"), "StudentId" : 7, "StudentName" : "Sam", "StudentAge" : 28 }
以下是获取 MongoDB 中不同记录值的方法。
案例 1 - 这里的字段是“StudentName”。
查询如下 -
> db.distinctRecordDemo.distinct("StudentName");
以下是显示 StudentName 不同记录的输出 -
[ "John", "Carol", "Sam", "Mike" ]
案例 2 - 这里的字段是“StudentAge”。
查询如下 -
> db.distinctRecordDemo.distinct("StudentAge");
以下是显示 StudentAge 不同记录的输出 -
[ 21, 22, 26, 24, 27, 28 ]
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