Mongo db CMD's

1) use dbName --- goes to selected db, if it not exist it will create a new db on that name.

2) db --- returns the name of the current db we selected

3) show dbs --- returns the list of dbs which contains any datas.

4) db.collectionName.insert(json object) --- inserts a data inside the selected collection name.

5) db.dropDatabase() --- drops the current database.

6)  db.createCollection("collectionName") --- creates new collection in a selected db.

7) show collections --- returns all exist collections.

8) db.collectionName.drop() --- drops the collection.

9) db.collectionName.find() --- returns all json objects in the collection.

10) db.collectionName.find({}, {"key": 1}) --- returns only the selected key and its value of all objects inside the collection.

11) db.collectionName.find({}, {"key": 0}) --- returns all the key value pairs except the selected key and its value of all the objects in the collection.

12) db.collectionName.find({}, {"key": 1, "key": 0}) --- multi functions.

13) db.collectionName.find({}, {"key": 1, "key2": 1, "key3": 0}).limit(3) --- returns the top 3(as mentioned in the limit parameter).

14) db.collectionName.find({}, {"key": 1, "key2": 1, "key3": 0}).skip(3) --- skips the top 3(as mentioned in the skip parameter).

15) db.collectionName.find({}, {"key": 1, "key2": 1, "key3": 0}).skip(3).limit(2)

16) db.collectionName.find({}, {"key": 1, "key2": 1, "key3": 0}).sort({"key": 1}) --- sorts the objects based on the selected key's values in assending(1) or dessending(-1).

17) db.collectionName.findOne({"key": value}) --- returns particular object.

18) db.collectionName.ensureIndex({"key": 1}) --- creates the index for our selected collection to make search data in large collection.

19) db.collectionName.dropIndex({"key": 1}) --- removes the index for the collection.

20) db.collectionName.aggregate([{$group: {_id: "$key", Result: {$sum: 1} } }]) --- sums the data based on the key and returns the each keys count.