mongodb

var c = db.collection.find()
var doc = function() {return c.hasNext() ? c.next() : null;}
c.objsLeftInBatch()

-projection
db.collection.find({rated: 'PG'}, {title: 1, -id: 0}).pretty()

-comparison query operators
$eq $gt $gte $in $lt $lte $ne $nin
db.collection.find({rated: {$in: ['G', 'PG']}}, {title: 1, rated: 1, _id: 0})

-element
$exists $type
db.collection.find({'tomato.meter': {$exists: true})
db.collection.find({'_id': {$type: 'string'}}).count()

-logical
$or $and $not $nor
db.collection.find( { $or: [ { '': {} }, { '': {} } ] } )

$regex
db.collection.find( { "": { $regex: } } )

-array
$all $elemMatch $size
db.collection.find( { genres: { $all: ["", "", ""] } } )

-update
db.collection.updateOne( {title: "the martian"}, { $set: { poster: } } )

db.collection.replaceOne()

db.collection.find( { runtime: { $gt:90, $lt:120 }}, { _id:0, title:1, runtime:1 } )

mongoimport
show dbs
use 'db'