A group of lights by

The by group is a SQL function. The reason SQL cannot execute data in real time is because this method does not scale. Mongo provides similar functionality, but once again, it doesn't scale . You can see the pattern here why Firebase doesn't provide such a request function.

It would be very helpful if you could provide some context for what you are actually trying to accomplish here, what the application rules are and which approaches you ruled out, not just your intended group decision.There are probably other, possibly better alternatives. See Problem XY .

Here are a couple of general alternatives obtained by making radical assumptions about your use case.

Saving totals

This is the most scalable solution. Save the data as follows:

/playbacks/$id/<playback data>
/group_totals/$group/<count>

      

        
        
        
      

    

When recording for playback, also update the counter for the corresponding group:

var fb = new Firebase(URL);
function addPlayback(rec) {
   var ref = fb.child('playbacks').push(rec, function(err) {
      if( err )  throw err;
      incrementCount(rec.data);
   });
}

function incrementCount(count) {
   fb.child('group_totals/' + count).transaction(function(currentVal) {
     return (currentVal||0)+1;
   });
}

      

        
        
        
      

    

Now when you want to get the total for a group, you can simply look at the value in group_totals / $ group. Likewise, you can store IDs for posts belonging to each group and use this index to grab only the posts for that group.

Use priorities for retrieval and grouping

A simpler approach is to give each record a priority based on the group / data value.

var fb = new Firebase(URL);
function addPlayback(rec) {
   rec['.priority'] = rec.data;
   var ref = fb.child('playbacks').push(rec, function(err) {
      if( err )  throw err;
   });
}

      

        
        
        
      

    

Now, to grab the recordset for a given group:

var fb = new Firebase(URL);
function getGroup(groupValue, callback) {
   fb.child('playbackPosition').startAt(groupValue).endAt(groupValue).once('value', callback);
}

function logGroupCount(groupValue, callback) {
   getGroup(groupValue, function(snap) {
       console.log('there are ' + snap.numChildren() + ' items in group ' +groupValue);
   });
}