Question

A Key-value store does not support Secondary Indexes.

Answer 1

Secondary index a framework of data which has a subset of attributes from some "parent" table.  

This "parent" table in originality is known as base table because the secondary index table is constructed directly from it.

Big advantage of the secondary index is that it is used in different separations and sort keys than base table.  

It can also use only a part of the base table's columns.

Answer 2

The statement is wrong, a key value can actually use to support the secondary indexes. The demo code that shows the use is,

function(value, keyData, arg){

 var data = Riak.mapValuesJson(value)[0];

 if (data.Birthdate == '1976-07-04' && data.LastName = 'Smith') {

   return [ data ];

 }

}

Here we have mentioned key, bucket name and a value.