How to replace Select distinct(empId) from Employee in Cloudant?

Question

I have a requirement to get only distinct Employee Ids from Employee table. My emit is .. emit(doc.empId,1), will give me all employee ids ie duplicates one also. How i can achieve the same in cloudant. If i use the reduce on value will it return me all Distinct employee ids?

Answer 1

you can use the Reduce function to obtain the distinct employee Ids.

see duplicate question: How do I do the SQL equivalent of "DISTINCT" in CouchDB?

if you are not interested in the value it could be simply

Map function

function (doc) {
    emit(doc.empId, null);
}

Reduce function

function (key, values, rereduce) {
    return null;
}

however, if you need to return values you can try something like this

Map

function (doc) {
  emit([doc.empId, doc.joiningDate], {"companyId": doc.companyId, "dept": doc.dept});
}

Reduce

function (keys, values, rereduce) {
  return values[0];
}

however, you need to make sure the values argument in the Reduce function is an array of all the objects emitted in the Map function. therefore, you will need to determine how best to

reduce to a single scalar value. That is, an integer; a string; or a small, fixed-size list or object that includes an aggregated value (or values) from the values argument.

from http://guide.couchdb.org/draft/cookbook.html

in my example, above i simply just took the first entry from values (i am assuming all the emitting values are identical).