SQLite按3个字段排序，每个类别返回前1个

public Cursor fetchAllPBs() {       
    String sql = "SELECT * FROM " + CAPTURES_TABLE + " GROUP BY " + KEY_CAPTURES_SPECIES 
            + " ORDER BY " + KEY_CAPTURES_POUNDS + " DESC, " + KEY_CAPTURES_OUNCES + " DESC, " + KEY_CAPTURES_DRAMS + " DESC;";
    Cursor c = mDb.rawQuery(sql, null);
    if(c != null) {
        c.moveToFirst();
    }
    return c;
}
public Cursor fetchAllPBs() {       
    String