Template
single collection
multiple collections
mgodatagen
update
indexe
explain
Stage
Database
bson
mgodatagen
[{"name":"John","age":10},{"name":"Jack","age":20},{"name":"Tom","age":30},{"name":"Lisa"}]
Query
db.collection.find({$or:[{age:{$gt:13,$lt:27}},{age:null},{age:{$exists:false}}]})
Result