Summing values by a date range. For @dj_agiledev :D

design_doc.js

{
  _id: '_design/queries',
  views: {
    sum_by_date: {
      map: function (doc) {
        if (doc.created_at) {
          // normalize doc.created_at into an integer timestamp
          // in this case, milliseconds since epoch
          var date = new Date(doc.created_at).getTime();
          emit(doc.created_at, doc.VALUE_YOU_WANT_TO_SUM);
        }
      },
      reduce: '_sum'
    }
  }
}

the query

GET http://localhost:5984/DATABASE/_design/queries/_view/sum_by_date?startkey=START_TIMESTAMP&endkey=END_TIMESTAMP

Custom reduce FTW!

I think this is better accomplished by using a built-in reduce and a different key order:

 var date = new Date(doc.date);
 var key = [doc.user_id, date.getUTCFullYear(), date.getUTCMonth() + 1, date.getUTCDate()];
 return emit(key, doc.pay);

With a query across dates I get back a result for each user for each day that matches my start and end keys. Is there a way to squash it down even further?

 _view/by_date?group_level=4&startkey=[user_id, 2013,1,14]&endkey=[user_id, 2013,2,15]

Built-in reduces have strong performance gains, are less error prone, and allow you to neat things like:

 emit(key, [doc.pay, doc.hours, ..., <some other numbers>]);

And, then _sum will go and sum each element of the array, etc.