PostgreSQL完成按月累加

PostgreSQL完成按月累加

背景

統計某個指標，指標按照月進行累加，注意需要按省份和年份進行分組。

方法一、使用自關聯

-- with 按月統計得到中間結果
WITH yms AS (SELECT regionid,SUM(getnum) AS getnum,SUM(dealnum) AS dealnum,to_char(qndate,'yyyy-MM') AS yearmonth
FROM t_queuenumber
GROUP BY regionid,to_char(qndate,'yyyy-MM')
ORDER BY regionid,yearmonth)

-- 查用子查詢解決。
SELECT s1.regionid,s1.yearmonth, getnum,dealnum,
(SELECT SUM(getnum) FROM yms  s2 WHERE s2.regionid = s1.regionid AND s2.yearmonth <= s1.yearmonth  AND SUBSTRING(s1.yearmonth,0,5) = SUBSTRING(s2.yearmonth,0,5) ) AS getaccumulatednum,
(SELECT SUM(dealnum) FROM yms  s2 WHERE s2.regionid = s1.regionid AND s2.yearmonth <= s1.yearmonth  AND  SUBSTRING(s1.yearmonth,0,5) = SUBSTRING(s2.yearmonth,0,5) ) AS accumulatednum
FROM yms s1;

查詢的結果如下：

方法二、使用窗口函數

更多關於窗口函數的用法，可以參考以前的文章。窗口函數十分適合這樣的場景：

	WITH yms AS (SELECT regionid,SUM(getnum) AS getnum,SUM(dealnum) AS dealnum,to_char(qndate,'yyyy-MM') AS yearmonth
	FROM t_queuenumber
	GROUP BY regionid,to_char(qndate,'yyyy-MM')
	ORDER BY regionid,yearmonth)
	-- 窗口函數的使用
	SELECT regionid,yearmonth,
	SUM(getnum) OVER(PARTITION BY regionid,SUBSTRING(yearmonth,0,5) ORDER BY yearmonth) AS getaccumulatednum,
	SUM(dealnum) OVER(PARTITION BY regionid ,SUBSTRING(yearmonth,0,5) ORDER BY yearmonth)  AS dealaccumulatednum
	FROM yms; 

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後記

可以使用子查詢、可以使用窗口函數完成上面業務場景。