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

couchdb

Solution

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);
}

Problem

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 datasets with the following: Map: ``` function(doc) { emit(doc.name, doc); } ``` Reduce: ``` function(keys, values, rereduce){ return values.length; } ``` Which I thought worked, returning something like: ``` "super fun C" 2 "super fun D" 2 "super fun E" 2 "super fun F" 18 ``` ... but not really. When I add a record, this count varies wildly. Sometimes the count actually decreases, which was very surprising. Am I doing something wrong? Maybe I don't fully understand the concept of eventual consistency?

Original source