Clickhouse实现累计求和cumulative sum

源表数据如下：

time	province	order_cnt
20200601	shandong	100
20200601	jiangsu	200
20200601	zhejiang	300
20200602	shandong	200
20200602	jiangsu	300
20200602	zhejiang	400
20200603	shandong	400
20200603	jiangsu	500
20200603	zhejiang	600

需求是按照省份和时间分类，每天累计求和，需求的结果如下：
（每天的数据都要按照省份将之前的订单数目进行累加）

time	province	order_cnt_sum
20200601	shandong	100
20200601	jiangsu	200
20200601	zhejiang	300
20200602	shandong	300
20200602	jiangsu	500
20200602	zhejiang	700
20200603	shandong	700
20200603	jiangsu	1000
20200603	zhejiang	1300

需要借助clickhouse的array系列函数实现: ArrayFunction

SELECT
    time,
    province,
    arraySum(arraySlice(order_cnts, 1, i)) AS order_cnt_sum  
FROM
(
    SELECT groupArray(order_cnt) AS order_cnts,
           groupArray(time) AS times,
           groupArray(province) AS provinces
    FROM
    (
        SELECT *
        FROM test_table order by time
    ) group by province
)
ARRAY JOIN
    times as time,
    provinces AS province,
    arrayEnumerate(order_cnts) AS i;