本文實(shí)例講述了mysql滑動(dòng)聚合/年初至今聚合原理與用法。分享給大家供大家參考,具體如下:
滑動(dòng)聚合是按順序?qū)瑒?dòng)窗口范圍內(nèi)的數(shù)據(jù)進(jìn)行聚合的操作。下累積聚合不同,滑動(dòng)聚合并不是統(tǒng)計(jì)開(kāi)始計(jì)算的位置到當(dāng)前位置的數(shù)據(jù)。
這里以統(tǒng)計(jì)最近三個(gè)月中員工第月訂單情況為例來(lái)介紹滑動(dòng)聚合。
滑動(dòng)聚合和累積聚合解決方案的主要區(qū)別在于連接的條件不同?;瑒?dòng)聚合條件不再是b.ordermonth = a.ordermonth,而應(yīng)該是b.ordermonth大于前三個(gè)月的月份,并且小于當(dāng)前月份。因此滑動(dòng)聚合的解決方案的SQL語(yǔ)句如下
SELECT
a.empid,
DATE_FORMAT(a.ordermonth, '%Y-%m') AS ordermonth,
a.qty AS thismonth,
SUM(b.qty) AS total,
CAST(AVG(b.qty) AS DECIMAL(5,2)) AS avg
FROM emporders a
INNER JOIN emporders b
ON a.empid=b.empid
AND b.ordermonth > DATE_ADD(a.ordermonth, INTERVAL -3 MONTH)
AND b.ordermonth = a.ordermonth
WHERE DATE_FORMAT(a.ordermonth,'%Y')='2015' AND DATE_FORMAT(b.ordermonth,'%Y')='2015'
GROUP BY a.empid,DATE_FORMAT(a.ordermonth, '%Y-%m'),a.qty
ORDER BY a.empid,a.ordermonth
運(yùn)行結(jié)果如下
該解決方案返回的是三個(gè)月為一個(gè)周期的滑動(dòng)聚合,但是每個(gè)用戶包含前兩個(gè)月并且未滿3個(gè)月的聚合。如果只希望返回滿3個(gè)月的聚合,不返回未滿3個(gè)月的聚合,可以使用HAVING過(guò)濾器進(jìn)行過(guò)濾,過(guò)濾的條件為MIN(b.ordermonth)=DATE_ADD(a.ordermonth, INTERVAL -2 MONTH),例如
SELECT
a.empid,
a.ordermonth AS ordermonth,
a.qty AS thismonth,
SUM(b.qty) AS total,
CAST(AVG(b.qty) AS DECIMAL(5,2)) AS avg
FROM emporders a
INNER JOIN emporders b
ON a.empid=b.empid
AND b.ordermonth > DATE_ADD(a.ordermonth, INTERVAL -3 MONTH)
AND b.ordermonth = a.ordermonth
WHERE DATE_FORMAT(a.ordermonth,'%Y')='2015' AND DATE_FORMAT(b.ordermonth,'%Y')='2015' AND a.empid=1
GROUP BY a.empid,DATE_FORMAT(a.ordermonth, '%Y-%m'),a.qty
HAVING MIN(b.ordermonth)=DATE_ADD(a.ordermonth, INTERVAL-2 MONTH)
ORDER BY a.empid,a.ordermonth
運(yùn)行結(jié)果如下
年初至今聚合和滑動(dòng)聚合類似,不同的地方僅在于統(tǒng)計(jì)的僅為當(dāng)前一年的聚合。唯一的區(qū)別體現(xiàn)在下限的開(kāi)始位置上。在年初至今的問(wèn)題中,下限為該年的第一天,而滑動(dòng)聚合的下限為N個(gè)月的第一天。因此,年初至今的問(wèn)題的解決方案如下圖所示,得到的結(jié)果
SELECT
a.empid,
DATE_FORMAT(a.ordermonth, '%Y-%m') AS ordermonth,
a.qty AS thismonth,
SUM(b.qty) AS total,
CAST(AVG(b.qty) AS DECIMAL(5,2)) AS avg
FROM emporders a
INNER JOIN emporders b
ON a.empid=b.empid
AND b.ordermonth >= DATE_FORMAT(a.ordermonth, '%Y-01-01')
AND b.ordermonth = a.ordermonth
AND DATE_FORMAT(b.ordermonth,'%Y')='2015'
GROUP BY a.empid,a.ordermonth,a.qty
ORDER BY a.empid,a.ordermonth
運(yùn)行結(jié)果如下
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