Mongodb group and sort

Question

How can I translate the following Sql query for Mongo?:

select a,b,sum(c) csum from coll wh         


        

Answer 1

I built up a histogram and what I did with version 2.2.2 was:

answer = db.coll.group(...)
db.histo.insert(answer)
db.histo.find().sort({ field: 1 })

At this point, if you don't need it, just db.histo.drop().

You can also avoid the variable and do:

db.histo.insert(db.coll.group(...))
db.histo.ensureIndex({ field: 1 })

Answer 2

db.coll.group(
       {key: { a:true, b:true },
        cond: { active:1 },
        reduce: function(obj,prev) { prev.csum += obj.c; },
        initial: { csum: 0 }
        });

You can execute it in MongoDB