Mongo

<p>db.yourCollectionName.aggregate([ { $project: { keys: { $objectToArray: &quot;$$ROOT&quot; } } }, { $unwind: &quot;$keys&quot; }, { $group: { _id: null, allKeys: { $addToSet: &quot;$keys.k&quot; } } }, { $project: { _id: 0, allKeys: 1 } } ])</p>