MongoDB allows you to select and filter documents using the aggregation pipeline framework. The Aggregation page in the MongoDB documentation provides additional examples of function calls.
The following table displays some examples of the query syntax and structure you can use to request data from MongoDB:
| Query expression | Description |
|---|---|
| { $match : {state : "FL", city : "ORLANDO" } }, {$sort : {pop : -1 } } | Returns all fields from all documents where the state field has a value of FL and the city field has a value of ORLANDO. The returned documents will be sorted by the pop field in descending order. |
| { $group : { _id: "$state"} }, { $sort : { _id : 1 } } | Returns one field named _id containing the distinct values for state in ascending order. This is similar to the SQL statement SELECT DISTINCT state AS _id FROM collection ORDER BY state ASC. |
| { $match : {state : "FL" } }, { $group: {_id: "$city" , pop: { $sum: "$pop" } } }, { $sort: { pop: -1 } }, { $project: {_id : 0, city : "$_id" } } | Returns all documents where the state field has a value of FL, aggregates all values of pop for each city, sorts by population descending, and returns one field named city. |
| { $unwind : "$result" } | Peels off the elements of an array individually, and returns one document for each element of the array. |