How do I retrieve an average from SQLite?

Question

I want to get the average value of a selection of a column. I'm trying to use SQL's AVG(X) function, but am not sure how. Here's what I've tried, but I get a CursorIndexOutOfBoundsException when calling c.getDouble(0). How should I do this?

    String q = "SELECT AVG(" + KEY_PERCENT_GRADE + ") FROM " + TABLE_GRADES 
                    + " WHERE " + KEY_CATEGORY_ID 
                    + " = '" + catId +"'";  //catId is an int
            Cursor c = db.rawQuery(q,null); 
            double d = c.getDouble(0); 

Answer 1

You should always moveToFirst() the cursor before accessing its content.

By doing so, there wouldn't be any problems even if the cursor returned 0 row.