Database

[{"collection":"empleados","count":50,"content":{"_id":{"type":"objectId"},"nombre":{"type":"faker","method":"FirstName"},"apellidos":{"type":"faker","method":"LastName"},"salario":{"type":"double","minDouble":950.0,"maxDouble":3000.0,"nullPercentage":10}}}]

Query

db.empleados.aggregate([{"$group":{"_id":null,"suma":{"$sum":"$salario"}}},{"$project":{"_id":0}}])

Result