Question

m new to android. When i m using db.query to retrieve and compare username it always returning some value
it have to return null when value not matches.

here is code

public boolean check(String name)
{
    SQLiteDatabase db = DB.getReadableDatabase();


      Cursor cursor = null;
      try{
      cursor=db.rawQuery("SELECT * FROM "+ DBHelper.Login_Table + " WHERE "+ 
              DBHelper.KEY_USERNAME + "='" + name + "'",null);

      }
      catch(Exception e)

      {
       e.printStackTrace();
      }

        if (cursor!=null) {
            Log.i("someTAG","Error .. USERNAME EXIST");
            cursor.moveToFirst();
            return true;

        }
        else
        {
            Log.i("someTAG","Error ..  NOT EXIST");
            return false;

      }
}

Answer 1

No, your cursor does not have to return null, it just has to return 0 records.

if(cursor.getCount() != 0){
    // user exists
} else {
    // user doesn't exist
}