What is the CouchDB equivalent of the SQL COUNT(*) aggregate function?

Question

Yep, I\'m a SQL jockey (sorta) coming into the CouchDb Map/Reduce world. I thought I had figured out how the equivalent of the COUNT(*) SQL aggregator function for CouchDB d

Answer 1

It looks like your reduce results are being re-reduced. That is, reduce is called more than once for each key and then called again with those results. You can handle that with a reduce function like this:

function(keys, values, rereduce) {
  if (rereduce) {
    return sum(values);
  } else {
    return values.length;
  }
}

Alternatively, you can change the map function so that the values are always a count of documents:

// map
function(doc) {
  emit(doc.name, 1);
}

// reduce
function(keys, values, rereduce) {
  return sum(values);
}

Answer 2

In your reduce just put:

_count

You can also get a sum using:

_sum

so basically reduce: "_sum" or reduce: "_count" and make sure the value your map emits is a valid integer (numeric value)

See "Built in reduce functions".