How to select a single field for all documents in a MongoDB collection?

Question

In my MongoDB, I have a student collection with 10 records having fields name and roll. One record of this collection is:

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Answer 1

Just for educational purposes you could also do it with any of the following ways:

1.

    var query = {"roll": {$gt: 70};
    var cursor = db.student.find(query);
    cursor.project({"roll":1, "_id":0});

2.

    var query = {"roll": {$gt: 70};
    var projection = {"roll":1, "_id":0};
    var cursor = db.student.find(query,projection);

`

Answer 2

db.student.find({}, {"roll":1, "_id":0})

This is equivalent to -

Select roll from student

db.student.find({}, {"roll":1, "name":1, "_id":0})

This is equivalent to -

Select roll, name from student

Answer 3

If u want to retrieve the field "roll" only for all 10 records in the collections. Then try this.

In MongoDb :

db.students.find( { } , { " roll " : { " $roll " })

In Sql :

select roll from students

Answer 4

Use the Query like this in the shell:

1. Use database_name

e.g: use database_name

2. Which returns only assets particular field information when matched , _id:0 specifies not to display ID in the result

db.collection_name.find( { "Search_Field": "value" }, 
                  { "Field_to_display": 1,_id:0 }  )

Answer 5

I just want to add to the answers that if you want to display a field that is nested in another object, you can use the following syntax

db.collection.find( {}, {{'object.key': true}})

Here key is present inside the object named object

{ "_id" : ObjectId("5d2ef0702385"), "object" : { "key" : "value" } }

Answer 6

get all data from table

db.student.find({})

SELECT * FROM student

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get all data from table without _id

db.student.find({}, {_id:0})

SELECT name, roll FROM student

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get all data from one field with _id

db.student.find({}, {roll:1})

SELECT id, roll FROM student

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get all data from one field without _id

db.student.find({}, {roll:1, _id:0})

SELECT roll FROM student

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find specified data using where clause

db.student.find({roll: 80})

SELECT * FROM students WHERE roll = '80'

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find a data using where clause and greater than condition

db.student.find({ "roll": { $gt: 70 }}) // $gt is greater than 

SELECT * FROM student WHERE roll > '70'

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find a data using where clause and greater than or equal to condition

db.student.find({ "roll": { $gte: 70 }}) // $gte is greater than or equal

SELECT * FROM student WHERE roll >= '70'

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find a data using where clause and less than or equal to condition

db.student.find({ "roll": { $lte: 70 }}) // $lte is less than or equal

SELECT * FROM student WHERE roll <= '70'

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find a data using where clause and less than to condition

db.student.find({ "roll": { $lt: 70 }})  // $lt is less than

SELECT * FROM student WHERE roll < '70'

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