To get distinct values from a column, use distinct() in MongoDB. Let us first create a collection with documents −> db.demo128.insertOne({"Name":"Chris"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e30583d68e7f832db1a7f5d") } > db.demo128.insertOne({"Name":"David"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e30584068e7f832db1a7f5e") } > db.demo128.insertOne({"Name":"David"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e30584368e7f832db1a7f5f") } > db.demo128.insertOne({"Name":"Bob"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e30584668e7f832db1a7f60") } > db.demo128.insertOne({"Name":"Chris"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e30584c68e7f832db1a7f61") }Display all documents from a collection with the help of find() method −> db.demo128.find();This will produce the following output −{ "_id" : ... Read More

For this, use aggregate() in MongoDB. Let us first create a collection with documents −> db.demo126.insertOne( ...    { ...       "StudentDetails" : { ...          "Number" : 1, ...          "OtherDetails" : [ ...          { ...                "Name" : "Chris", ...                "Score" : 55 ... ...          } ...    ].. }} ... ); {    "acknowledged" : true,    "insertedId" : ObjectId("5e304b3068e7f832db1a7f56") } > > > db.demo126.insertOne( ...    { ... Read More

To remove a specific element, use $pull. Let us create a collection with documents −> db.demo125.insertOne({"ListOfNames":["John", "Chris", "Bob", "David", "Carol"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e2f304068e7f832db1a7f55") }Display all documents from a collection with the help of find() method −> db.demo125.find().pretty();This will produce the following output −{    "_id" : ObjectId("5e2f304068e7f832db1a7f55"),    "ListOfNames" : [       "John",       "Chris",       "Bob",       "David",       "Carol"    ] }Following is the query to remove a specific element from array in MongoDB −> db.demo125.update( ... { }, ... { $pull: ... Read More

For this, use find() along with update(). Let us create a collection with documents −> db.demo124.insertOne( ...    { ...       "Name" : "John", ...       "Id" : 101, ...       "ProjectDetails" : [{ ...          "ProjectName1" : "Online Book", ...          "ProjectName2" : "Online Banking" ...    }, { ...          "ProjectName1" : "Online Library Management System", ...          "ProjectName2" : "School Management System" ...       }] ...    } ... ); {    "acknowledged" : true,    "insertedId" ... Read More

Let us create a collection with documents −> db.demo123.insertOne({"ListOfSubject":['MySQL', 'MongoDB', 'Java']}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e2f24ac140daf4c2a3544b8") } > db.demo123.insertOne({"ListOfSubject":['Python', 'MongoDB', 'C']}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e2f24cd140daf4c2a3544b9") } > db.demo123.insertOne({"ListOfSubject":['MySQL', 'MongoDB', 'C++']}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e2f24ce140daf4c2a3544ba") }Display all documents from a collection with the help of find() method −> db.demo123.find();This will produce the following output −{ "_id" : ObjectId("5e2f24ac140daf4c2a3544b8"), "ListOfSubject" : [ "MySQL", "MongoDB", "Java" ] } { "_id" : ObjectId("5e2f24cd140daf4c2a3544b9"), "ListOfSubject" : [ "Python", "MongoDB", "C" ] } { "_id" : ObjectId("5e2f24ce140daf4c2a3544ba"), "ListOfSubject" : [ "MySQL", "MongoDB", ... Read More

To get distinct levels of array field, use $addToSet in MongoDB. Let us create a collection with documents −> db.demo122.insertOne({"ListOfValues":[100, 10]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e2f20f1140daf4c2a3544b6") } > db.demo122.insertOne({"ListOfValues":[240, 10]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e2f20f7140daf4c2a3544b7") }Display all documents from a collection with the help of find() method −> db.demo122.find();This will produce the following output −{ "_id" : ObjectId("5e2f20f1140daf4c2a3544b6"), "ListOfValues" : [ 100, 10 ] } { "_id" : ObjectId("5e2f20f7140daf4c2a3544b7"), "ListOfValues" : [ 240, 10 ] }Following is the query to get distinct levels of array field in MongoDB −> db.demo122.aggregate([ ...   ... Read More

Let us first create a collection with documents −> db.demo121.insertOne( ...    { ...       "Id" : 101, ...       "Details" : [ ...          { ...             "SubjectId" : "1", ...             "SubjectName" : "MongoDB", ...             "Score" : 76 ...          }, ...          { ...             "SubjectId" : "2", ...             "SubjectName" : "MySQL", ...         ... Read More

For this, use aggregate() in MongoDB. Let us create a collection with documents −> db.demo120.insertOne( ...    { ...       'Name': 'Chris', ...       'Subjects': [ 'MySQL', 'MongoDB', 'Java', 'Python' ] ...    } ... ); {    "acknowledged" : true,    "insertedId" : ObjectId("5e2f11aed8f64a552dae6365") } > db.demo120.insertOne( ...    { ...       'Name': 'Bob', ...       'Subjects': [ 'C', 'MongoDB' ] ...    } ... ); {    "acknowledged" : true,    "insertedId" : ObjectId("5e2f11afd8f64a552dae6366") }Display all documents from a collection with the help of find() method −> db.demo120.find();This will produce ... Read More

To prevent duplicates of multiple fields, use ensureIndex() and set unique:true. Let us create a collection with documents −> db.demo272.ensureIndex({"FirstName":1, "Subject":1}, {unique:true}); {    "createdCollectionAutomatically" : true,    "numIndexesBefore" : 1,    "numIndexesAfter" : 2,    "ok" : 1 } > db.demo272.insertOne({"FirstName":"Chris", "Subject":"MySQL"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e48232a1627c0c63e7dbabf") } > db.demo272.insertOne({"FirstName":"Chris", "Subject":"MongoDB"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e48232f1627c0c63e7dbac0") } > db.demo272.insertOne({"FirstName":"David", "Subject":"MySQL"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e48233a1627c0c63e7dbac1") } > db.demo272.insertOne({"FirstName":"Chris", "Subject":"MySQL"}); 2020-02-15T22:28:55.137+0530 E QUERY    [js] WriteError: E11000 duplicate key error collection: test.demo272 index: FirstName_1_Subject_1 dup key: { : ... Read More

Set a custom variable and use update() along with $inc to increment. Let us create a collection with documents −> db.demo271.insertOne({"Marks":56}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e4821211627c0c63e7dbabc") } > db.demo271.insertOne({"Marks":78}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e4821241627c0c63e7dbabd") } > db.demo271.insertOne({"Marks":72}); {    "acknowledged" : true,    "insertedId" : ObjectId("5e48212b1627c0c63e7dbabe") }Display all documents from a collection with the help of find() method −> db.demo271.find();This will produce the following output −{ "_id" : ObjectId("5e4821211627c0c63e7dbabc"), "Marks" : 56 } { "_id" : ObjectId("5e4821241627c0c63e7dbabd"), "Marks" : 78 } { "_id" : ObjectId("5e48212b1627c0c63e7dbabe"), "Marks" : 72 }Following is the query ... Read More