Database
[{Campaign_Name:"Winback",Basecount:2,Actcount:3},{Campaign_Name:"Winback",Basecount:6,Actcount:4},{Campaign_Name:"Winback",Basecount:4,Actcount:8},{Campaign_Name:"base",Basecount:9,Actcount:3},{Campaign_Name:"base",Basecount:2,Actcount:3},{Campaign_Name:"base",Basecount:22,Actcount:3},{Campaign_Name:"base",Basecount:1,Actcount:3},{Campaign_Name:"base",Basecount:7,Actcount:3}]
Query
db.collection.aggregate([{$group:{_id:"$Campaign_Name",Basecount:{$sum:{$cond:[{$eq:["$Campaign_Name","Winback"]},"$Actcount","$Basecount"]}}}}])