SUM功能无法识别

Question

我试图构建一个查询，它会检索传入呼叫持续时间的总和。 问题是SUM（）无法识别。 错误消息为Invalid Column SUM(DURATION)。 谢谢。 这是我的代码：

    String[] columns = {"SUM("+CallLog.Calls.DURATION+")"};
    String selection = CallLog.Calls.DATE+" >= ? and "+CallLog.Calls.TYPE+" =    "+CallLog.Calls.INCOMING_TYPE;
    String[] args = { String.valueOf(lastMonthMillis) };

    Cursor cursor = resolver.query(CallLog.Calls.CONTENT_URI, columns,
            selection, args, CallLog.Calls.DATE);

我试过这样：

String[] projection = { CallLog.Calls.DURATION, CallLog.Calls.TYPE,
            CallLog.Calls.DATE, "SUM(" + CallLog.Calls.DURATION + ")" };
    String selection = CallLog.Calls.TYPE + " = ? and "
            + CallLog.Calls.DATE + " >= ?";
    String[] selectionArgs = { String.valueOf(CallLog.Calls.OUTGOING_TYPE),
            String.valueOf(lastMonthMillis) };
    String sortOrder = CallLog.Calls.DATE+" DESC";
    Cursor cursor = resolver.query(CallLog.Calls.CONTENT_URI, projection,   selection, selectionArgs, sortOrder);

错误是Invalid Column SUM(DURATION)，因此可以识别持续时间？ 有什么建议吗？