mysql - How to get distinct result in Mongo DB? -

i using mongodb 2.6.5. have books collection.

   > db.books.find()   { "_id" : "5476f8b5e4b04367d6c95010", "author" : "abc", "title" : "xyz", "isbnno" : "9781887902991", "category" : "computer" }   { "_id" : "5476fae0e4b0016adffd08e4", "author" : "bcd", "title" : "uvw", "isbnno" : "9781887902991", "category" : "computer" }   { "_id" : "5476fb7ce4b0016adffd08e5", "author" : "cde", "title" : "pqr", "isbnno" : "9781887902991", "category" : "biography" }  

i want result :

{ "_id" : "5476fae0e4b0016adffd08e4", "author" : "bcd", "title" : "uvw", "isbnno" : "9781887902991", "category" : "computer" }   { "_id" : "5476fb7ce4b0016adffd08e5", "author" : "cde", "title" : "pqr", "isbnno" : "9781887902991", "category" : "biography" }  

i mean 1 book each category “group category” in mysql.

how can achieve this?

thanks in advance.

you need use aggregate pipeline $group , $project operators.

• group based on category.
• pick values of first record in each group.
• project record each group.

the code:

db.books.aggregate([ {$group:{"_id":"$category",          "author":{$first:"$author"},          "title":{$first:"$title"},          "isbnno":{$first:"$isbnno"},          "category":{$first:"$category"}}}, {$project:{"_id":0,"author":1,            "title":1,"isbnno":1,"category":1}} ])