To count array elements from a specific field, use $size in MongoDB. Let us create a collection with documents −> db.demo723.insertOne({"Subject":["MySQL", "MongoDB"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5eab094d43417811278f588a") } > db.demo723.insertOne({"Subject":["C"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5eab095243417811278f588b") } > db.demo723.insertOne({"Subject":["C++", "Java", "Python"]}); {    "acknowledged" : true,    "insertedId" : ObjectId("5eab095f43417811278f588c") }Display all documents from a collection with the help of find() method −> db.demo723.find();This will produce the following output −{ "_id" : ObjectId("5eab094d43417811278f588a"), "Subject" : [ "MySQL", "MongoDB" ] } { "_id" : ObjectId("5eab095243417811278f588b"), "Subject" : [ "C" ] } { "_id" : ... Read More

To ignore null values in MongoDB, use "$ne" : null in aggregate(). Let us create a collection with documents −> db.demo722.insertOne( ...    { ...       id:101, ...       details: [ ...          { Name:""}, ...          { Name: "David"}, ...          {Name:null}, ...          {Name:"Carol"} ...       ] ...    } ... ); {    "acknowledged" : true,    "insertedId" : ObjectId("5eab07d543417811278f5889") }Display all documents from a collection with the help of find() method −> db.demo722.find();This will produce the following output ... Read More

To count by multiple fields, use $facet in MongoDB. The $facet processes multiple aggregation pipelines within a single stage on the same set of input documents. Let us create a collection with documents −> db.demo721.insertOne( ...    { ... ...       "details1": { ...          "id":101 ... ...       }, ...       "details2": { ...          "id":101 ...       }, ...       "details3": { ...          "id":101 ...       } ...    } ... ); {    "acknowledged" : ... Read More

To update all the values, use update() along with multi:true. Let us create a collection with documents −> db.demo720.insertOne({"SubjectName":"MySQL"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5eaae7ca43417811278f5883") } > db.demo720.insertOne({"SubjectName":"Java"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5eaae7ce43417811278f5884") } > db.demo720.insertOne({"SubjectName":"C"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5eaae7d143417811278f5885") } > db.demo720.insertOne({"SubjectName":"C++"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5eaae7d543417811278f5886") }Display all documents from a collection with the help of find() method −> db.demo720.find();This will produce the following output −{ "_id" : ObjectId("5eaae7ca43417811278f5883"), "SubjectName" : "MySQL" } { "_id" : ObjectId("5eaae7ce43417811278f5884"), "SubjectName" : "Java" } { ... Read More

To add a new field, use the $addFields in MongoDB. Let us create a collection with documents −> db.demo719.insertOne( ...    { ...       "Number":"7374644", ...       "details" : { ...          "otherDetails" : [ ...             { ...                "ProductId" :"102", ...                "ProductPrice" : NumberInt(500) ...             }, ...             { ...                "ProductId" :"103", ...     ... Read More

The task is to convert the distance from kilometers to meters and centimeters in PL/SQL.PL/SQL is the extension of SQL which combines the Data manipulation of SQL with the working of procedural language.According to the problem we should have distance in kilometers whose value we have to convert in meters and centimeters.As per the conversion rule −1km = 1000 meters1km = 100000 centimetersAccording to this conversion rule we want the distance to be converted by a logic in PL/SQL.ExampleInput: kilometer = 10 Output: meter = 10000    Centimeter = 1000000 Input: kilometer = 9 Output: meter = 9000    Centimeter ... Read More

To display only unique records, use distinct() in MongoDB. Let us create a collection with documents −> db.demo613.insertOne({"Name":"Chris"});{    "acknowledged" : true, "insertedId" : ObjectId("5e988bd4f6b89257f5584d88") } > db.demo613.insertOne({"Name":"Bob"});{    "acknowledged" : true, "insertedId" : ObjectId("5e988bdbf6b89257f5584d89") } > db.demo613.insertOne({"Name":"Bob"});{    "acknowledged" : true, "insertedId" : ObjectId("5e988bddf6b89257f5584d8a") } > db.demo613.insertOne({"Name":"David"});{    "acknowledged" : true, "insertedId" : ObjectId("5e988be0f6b89257f5584d8b") } > db.demo613.insertOne({"Name":"Chris"});{    "acknowledged" : true, "insertedId" : ObjectId("5e988be2f6b89257f5584d8c") } > db.demo613.insertOne({"Name":"Sam"});{    "acknowledged" : true, "insertedId" : ObjectId("5e988be8f6b89257f5584d8d") }Display all documents from a collection with the help of find() method −> db.demo613.find();This will produce the following output −{ "_id" : ObjectId("5e988bd4f6b89257f5584d88"), "Name" : ... Read More

Check for a specific field using MongoDB $exists. If that field does not exist in a document, then you need to display the same document with find().Let us create a collection with documents −> db.demo612.insertOne({id:1, "Info":[{Name:"Chris", Age:21}, {Name:"David"}]});{    "acknowledged" : true, "insertedId" : ObjectId("5e987372f6b89257f5584d87") }Display all documents from a collection with the help of find() method −> db.demo612.find().pretty();This will produce the following output −{    "_id" : ObjectId("5e987372f6b89257f5584d87"),    "id" : 1,    "Info" : [       {          "Name" : "Chris",          "Age" : 21       },   ... Read More

To sort documents in MongoDB 4, use sort(). To show only a single field, which is sorted, set it to 1.Let us create a collection with documents −> db.demo611.insertOne({"Name":"Chris"});{    "acknowledged" : true, "insertedId" : ObjectId("5e987110f6b89257f5584d83") } > db.demo611.insertOne({"Name":"Adam"});{    "acknowledged" : true, "insertedId" : ObjectId("5e987115f6b89257f5584d84") } > db.demo611.insertOne({"Name":"John"});{    "acknowledged" : true, "insertedId" : ObjectId("5e987118f6b89257f5584d85") } > db.demo611.insertOne({"Name":"Bob"});{    "acknowledged" : true, "insertedId" : ObjectId("5e98711bf6b89257f5584d86") }Display all documents from a collection with the help of find() method −> db.demo611.find(); This will produce the following output: { "_id" : ObjectId("5e987110f6b89257f5584d83"), "Name" : "Chris" } { "_id" : ObjectId("5e987115f6b89257f5584d84"), "Name" : ... Read More

To add together a subset of elements of an array, use $first along with $sum. Let us create a collection with documents −> db.demo610.insertOne({Values:[10, 20, 30, 40, 50]});{    "acknowledged" : true, "insertedId" : ObjectId("5e9747b8f57d0dc0b182d62e") }Display all documents from a collection with the help of find() method −> db.demo610.find().pretty()This will produce the following output −{    "_id" : ObjectId("5e9747b8f57d0dc0b182d62e"),    "Values" : [       10,       20,       30,       40,       50    ] }Here is the query to add together a subset of elements of an array in ... Read More