Database
[{"commandName":"migration_a","executionDate":ISODate("1998-11-04T18:46:14.000Z")},{"commandName":"migration_a","executionDate":ISODate("1970-05-09T20:16:37.000Z")},{"commandName":"migration_a","executionDate":ISODate("2005-11-08T11:58:52.000Z")},{"commandName":"migration_b","executionDate":ISODate("2016-06-02T19:48:34.000Z")}]
Query
db.collection.aggregate([{$group:{"_id":"$commandName","executionDate":{"$last":"$executionDate"}}}])