Order By with duration strings having time units

I have found some information and pointers here. Extracts from that thread:

...retrieved records from a given collection a parsed only once (FastJSON) and cached in-memory for fast retrieval. The cache is a O(1) hashtable so performance shouldn't be a problem.

...only the first retrieval is a little bit slower than the others since it involve a disk access (In case you are working with an on-disk DB) and a preprocessing phase (FastJSON decoding) while later fetches are in-memory operations only with no decoding overhead.

My Observations about document storage in UnQlite :

In memory: Store faster, search slower ;But both slower than SQLite!
In File: Store slower, search faster

e.g:- For same data, In UnQLite:

In mem: store: 901.9 ms, search: 2586 ms
In Local disk: store: 15223.3 ms , search: 114.2 ms

SQLite: In mem: Store 9507 ms , Search : 105 ms

Honestly, I haven't benchmarked SQLite indexes with UnQLite doc store. But, keep in mind that UnQLite is shipped with a disk KV storage engine that support nearly O(1) record retrieval.

The information given lacks specifics and context - nothing how the tests were conducted. Yet I believe it's enough to construct myself a vague opinion.

To me it seem that UnQLite has faster write but slower read performance, in relation to SQLite. It is probably a general trend when comparing SQL with NoSQL database systems.

Finally I found the solution to my own question

Following is the code which worked for me

DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        Date date = new Date();
        Calendar calendar = Calendar.getInstance();
        String startDate = dateFormat.format(date);
        String endDate = "";
        for (int i = 1; i <= 24; i++) {
            System.out.println("Start Date:- " + startDate);
            calendar.add(Calendar.HOUR_OF_DAY, -1);
            date = calendar.getTime();
            endDate = dateFormat.format(date);
            System.out.println("End Date:- " + endDate);
            String data = dbAdapter.getOutDoorHourlyData(startDate, endDate);
            System.out.println("Hourly Average:- " + data);
            startDate = endDate;
            endDate = "";
        }

public String getOutDoorHourlyData(String startDate, String endDate) {
        double outdoorHourly = 0;

        Cursor cursor = _sqliteDB.rawQuery("Select AVG("
                + COLOUMN_NAME + ") from (Select * FROM "
                + TABLE_NAME + " where " + COLOUMN_NAME + " >= '"
                + endDate + "' and " + COLOUMN_NAME + " < '" + startDate
                + "')", null);

        try {

            if (cursor != null) {
                if (cursor.getCount() > 0) {
                    cursor.moveToFirst();
                    do {
                        outdoorHourly = cursor.getDouble(0);
                    } while (cursor.moveToNext());
                }
                cursor.close();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }

        String hourlyData = decimalFormat.format(outdoorHourly);
        hourlyData = hourlyData.replace(",", ".");
        return hourlyData;

    }

 }

I hope it will help someone in future