12. MongoDB - CRUD operations - Part_II_Querying , Coursor {skip(),limit()}

#  limit()
Use the limit() method on a cursor to specify the maximum number of documents the cursor will return

#  skip()
Call the skip() method on a cursor to control where MongoDB begins returning results. This approach may be useful in implementing “paged” results.

> db.result.find()
{ "_id" : ObjectId("538de41d2110740e7c9a5373"), "student" : 1, "exam type" : "Exams", "score" : 69 }
{ "_id" : ObjectId("538de41d2110740e7c9a5374"), "student" : 1, "exam type" : "Essay", "score" : 92 }
{ "_id" : ObjectId("538de41d2110740e7c9a5375"), "student" : 1, "exam type" : "Quiz", "score" : 54 }
{ "_id" : ObjectId("538de41d2110740e7c9a5376"), "student" : 2, "exam type" : "Exams", "score" : 75 }
{ "_id" : ObjectId("538de41d2110740e7c9a5377"), "student" : 2, "exam type" : "Essay", "score" : 66 }
{ "_id" : ObjectId("538de41d2110740e7c9a5378"), "student" : 2, "exam type" : "Quiz", "score" : 59 }
{ "_id" : ObjectId("538de41d2110740e7c9a5379"), "student" : 3, "exam type" : "Exams", "score" : 12 }
{ "_id" : ObjectId("538de41d2110740e7c9a537a"), "student" : 3, "exam type" : "Essay", "score" : 15 }
{ "_id" : ObjectId("538de41d2110740e7c9a537b"), "student" : 3, "exam type" : "Quiz", "score" : 19 }
{ "_id" : ObjectId("538de41d2110740e7c9a537c"), "student" : 4, "exam type" : "Exams", "score" : 56 }
{ "_id" : ObjectId("538de41d2110740e7c9a537d"), "student" : 4, "exam type" : "Essay", "score" : 38 }
{ "_id" : ObjectId("538de41d2110740e7c9a537e"), "student" : 4, "exam type" : "Quiz", "score" : 74 }
{ "_id" : ObjectId("538de41d2110740e7c9a537f"), "student" : 5, "exam type" : "Exams", "score" : 55 }
{ "_id" : ObjectId("538de41d2110740e7c9a5380"), "student" : 5, "exam type" : "Essay", "score" : 24 }
{ "_id" : ObjectId("538de41d2110740e7c9a5381"), "student" : 5, "exam type" : "Quiz", "score" : 24 }
{ "_id" : ObjectId("538de41d2110740e7c9a5382"), "student" : 6, "exam type" : "Exams", "score" : 11 }
{ "_id" : ObjectId("538de41d2110740e7c9a5383"), "student" : 6, "exam type" : "Essay", "score" : 5 }
{ "_id" : ObjectId("538de41d2110740e7c9a5384"), "student" : 6, "exam type" : "Quiz", "score" : 59 }
{ "_id" : ObjectId("538de41d2110740e7c9a5385"), "student" : 7, "exam type" : "Exams", "score" : 3 }
{ "_id" : ObjectId("538de41d2110740e7c9a5386"), "student" : 7, "exam type" : "Essay", "score" : 5 }
Type "it" for more

/* hide '_id' filed  and find all documents */
> db.result.find({_id:false})
> db.result.find({},{_id:false})
{ "student" : 1, "exam type" : "Exams", "score" : 69 }
{ "student" : 1, "exam type" : "Essay", "score" : 92 }
{ "student" : 1, "exam type" : "Quiz", "score" : 54 }
{ "student" : 2, "exam type" : "Exams", "score" : 75 }
{ "student" : 2, "exam type" : "Essay", "score" : 66 }
{ "student" : 2, "exam type" : "Quiz", "score" : 59 }
{ "student" : 3, "exam type" : "Exams", "score" : 12 }
{ "student" : 3, "exam type" : "Essay", "score" : 15 }
{ "student" : 3, "exam type" : "Quiz", "score" : 19 }
{ "student" : 4, "exam type" : "Exams", "score" : 56 }
{ "student" : 4, "exam type" : "Essay", "score" : 38 }
{ "student" : 4, "exam type" : "Quiz", "score" : 74 }
{ "student" : 5, "exam type" : "Exams", "score" : 55 }
{ "student" : 5, "exam type" : "Essay", "score" : 24 }
{ "student" : 5, "exam type" : "Quiz", "score" : 24 }
{ "student" : 6, "exam type" : "Exams", "score" : 11 }
{ "student" : 6, "exam type" : "Essay", "score" : 5 }
{ "student" : 6, "exam type" : "Quiz", "score" : 59 }
{ "student" : 7, "exam type" : "Exams", "score" : 3 }
{ "student" : 7, "exam type" : "Essay", "score" : 5 }
Type "it" for more

/* hide '_id' filed  and display the first 5 documents */
> db.result.find({},{_id:false}).limit(5)
{ "student" : 1, "exam type" : "Exams", "score" : 69 }
{ "student" : 1, "exam type" : "Essay", "score" : 92 }
{ "student" : 1, "exam type" : "Quiz", "score" : 54 }
{ "student" : 2, "exam type" : "Exams", "score" : 75 }
{ "student" : 2, "exam type" : "Essay", "score" : 66 }

/* hide '_id' filed  and skip first 3 documents */

> db.result.find({},{_id:false}).skip(3)

{ "student" : 2, "exam type" : "Exams", "score" : 75 }

{ "student" : 2, "exam type" : "Essay", "score" : 66 }

{ "student" : 2, "exam type" : "Quiz", "score" : 59 }

{ "student" : 3, "exam type" : "Exams", "score" : 12 }

{ "student" : 3, "exam type" : "Essay", "score" : 15 }

{ "student" : 3, "exam type" : "Quiz", "score" : 19 }

{ "student" : 4, "exam type" : "Exams", "score" : 56 }

{ "student" : 4, "exam type" : "Essay", "score" : 38 }

{ "student" : 4, "exam type" : "Quiz", "score" : 74 }

{ "student" : 5, "exam type" : "Exams", "score" : 55 }

{ "student" : 5, "exam type" : "Essay", "score" : 24 }

{ "student" : 5, "exam type" : "Quiz", "score" : 24 }

{ "student" : 6, "exam type" : "Exams", "score" : 11 }

{ "student" : 6, "exam type" : "Essay", "score" : 5 }

{ "student" : 6, "exam type" : "Quiz", "score" : 59 }

{ "student" : 7, "exam type" : "Exams", "score" : 3 }

{ "student" : 7, "exam type" : "Essay", "score" : 5 }

{ "student" : 7, "exam type" : "Quiz", "score" : 92 }

{ "student" : 8, "exam type" : "Exams", "score" : 40 }

{ "student" : 8, "exam type" : "Essay", "score" : 85 }

Type "it" for more

/* hide '_id' filed  and skip first 3 document  display the 5 documents (4,5,6,7,8)*/

> db.result.find({},{_id:false}).skip(3).limit(5)

{ "student" : 2, "exam type" : "Exams", "score" : 75 }

{ "student" : 2, "exam type" : "Essay", "score" : 66 }

{ "student" : 2, "exam type" : "Quiz", "score" : 59 }

{ "student" : 3, "exam type" : "Exams", "score" : 12 }

{ "student" : 3, "exam type" : "Essay", "score" : 15 }

/* hide '_id' filed  and select 'score' lessthan equal 20 */

> db.result.find({score:{$lte:20}},{_id:false})

{ "student" : 3, "exam type" : "Exams", "score" : 12 }

{ "student" : 3, "exam type" : "Essay", "score" : 15 }

{ "student" : 3, "exam type" : "Quiz", "score" : 19 }

{ "student" : 6, "exam type" : "Exams", "score" : 11 }

{ "student" : 6, "exam type" : "Essay", "score" : 5 }

{ "student" : 7, "exam type" : "Exams", "score" : 3 }

{ "student" : 7, "exam type" : "Essay", "score" : 5 }

{ "student" : 8, "exam type" : "Quiz", "score" : 14 }

{ "student" : 9, "exam type" : "Quiz", "score" : 3 }

{ "student" : 12, "exam type" : "Exams", "score" : 20 }

{ "student" : 12, "exam type" : "Essay", "score" : 3 }

{ "student" : 13, "exam type" : "Essay", "score" : 18 }

{ "student" : 13, "exam type" : "Quiz", "score" : 5 }

{ "student" : 14, "exam type" : "Exams", "score" : 4 }

{ "student" : 15, "exam type" : "Exams", "score" : 4 }

{ "student" : 17, "exam type" : "Essay", "score" : 12 }

{ "student" : 18, "exam type" : "Essay", "score" : 3 }

{ "student" : 19, "exam type" : "Exams", "score" : 4 }

/* hide '_id' filed  , select 'score' lessthan equal 20 and count all document */

> db.result.find({score:{$lte:20}},{_id:false}).count()

18

/* hide '_id' filed  , select 'score' lessthan equal 20 and skip 10 documents */

> db.result.find({score:{$lte:20}},{_id:false}).skip(10)

{ "student" : 12, "exam type" : "Essay", "score" : 3 }

{ "student" : 13, "exam type" : "Essay", "score" : 18 }

{ "student" : 13, "exam type" : "Quiz", "score" : 5 }

{ "student" : 14, "exam type" : "Exams", "score" : 4 }

{ "student" : 15, "exam type" : "Exams", "score" : 4 }

{ "student" : 17, "exam type" : "Essay", "score" : 12 }

{ "student" : 18, "exam type" : "Essay", "score" : 3 }

{ "student" : 19, "exam type" : "Exams", "score" : 4 }

/* hide '_id' filed  , select 'score' lessthan equal 20 and skip 10 documents  limit 3 documents*/

> db.result.find({score:{$lte:20}},{_id:false}).skip(10).limit(3)

{ "student" : 12, "exam type" : "Essay", "score" : 3 }

{ "student" : 13, "exam type" : "Essay", "score" : 18 }

{ "student" : 13, "exam type" : "Quiz", "score" : 5 }