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mysql累積聚合原理與用法實(shí)例分析

更新時(shí)間：2019年12月27日 11:01:46 作者：雪山飛豬

這篇文章主要介紹了mysql累積聚合原理與用法,結(jié)合實(shí)例形式分析了mysql累積聚合原理、用法及相關(guān)操作注意事項(xiàng),需要的朋友可以參考下

本文實(shí)例講述了mysql累積聚合原理與用法。分享給大家供大家參考，具體如下：

累積聚合為聚合從序列內(nèi)第一個(gè)元素到當(dāng)前元素的數(shù)據(jù)，如為每個(gè)員工返回每月開始到現(xiàn)在累積的訂單數(shù)量和平均訂單數(shù)量

行號(hào)問題有兩個(gè)解決方案，分別是為使用子查詢和使用連接。子查詢的方法通常比較直觀，可讀性強(qiáng)。但是在要求進(jìn)行聚合時(shí)，子查詢需要為每個(gè)聚合掃描一次數(shù)據(jù)，而連接方法通常只需要掃描一次就可以得到結(jié)果。下面的查詢使用連接來(lái)得到結(jié)果

SELECT
 a.empid,
 a.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 <= a.ordermonth
GROUP BY a.empid,a.ordermonth,a.qty
ORDER BY a.empid,a.ordermonth

如果只是查詢2015年的累積訂單，可以加上以where條件

WHERE DATE_FORMAT(a.ordermonth,'%Y')='2015' AND DATE_FORMAT(b.ordermonth,'%Y')='2015'

運(yùn)行結(jié)果如下

此外可能還需要篩選數(shù)據(jù)，例如只需要返回每個(gè)員工到達(dá)某一目標(biāo)之前每月訂單的情況。這里假設(shè)統(tǒng)計(jì)每個(gè)員工的合計(jì)訂單數(shù)量達(dá)到1000之前的累積情況。

這里可以使用HAVING過(guò)濾器來(lái)完成查詢

SELECT
 a.empid,
 a.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 <= a.ordermonth
WHERE DATE_FORMAT(a.ordermonth,'%Y')='2015' AND DATE_FORMAT(b.ordermonth,'%Y')='2015'
GROUP BY a.empid,a.ordermonth,a.qty
HAVING total<1000
ORDER BY a.empid,a.ordermonth

這里并沒有統(tǒng)計(jì)到達(dá)到1000時(shí)該月的情況，如果要進(jìn)行統(tǒng)計(jì)，則情況又有點(diǎn)復(fù)雜。如果指定了total <= 1000，則只有該月訂單數(shù)量正好為1000才進(jìn)行統(tǒng)計(jì)，否則不會(huì)對(duì)該月進(jìn)行統(tǒng)計(jì)。因此這個(gè)問題的過(guò)濾，可以從另外一個(gè)方面來(lái)考慮。當(dāng)累積累積訂單小于1000時(shí)，累積訂單與上個(gè)月的訂單之差是小于1000的，同時(shí)也能對(duì)第一個(gè)訂單數(shù)量超過(guò)1000的月份進(jìn)行統(tǒng)計(jì)。故該解決方案的SQL語(yǔ)句如下

SELECT
 a.empid,
 a.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 <= a.ordermonth
WHERE DATE_FORMAT(a.ordermonth,'%Y')='2015' AND DATE_FORMAT(b.ordermonth,'%Y')='2015'
GROUP BY a.empid,a.ordermonth,a.qty
HAVING total-a.qty < 1000
ORDER BY a.empid,a.ordermonth

運(yùn)行結(jié)果如下

如果只想返回達(dá)到累積訂單數(shù)為1000的當(dāng)月數(shù)據(jù)，不返回之前的月份，則可以對(duì)上述SQL語(yǔ)句

進(jìn)一步過(guò)濾，再添加累積訂單數(shù)量大于等于1000的條件。該問題的SQL語(yǔ)句如下，

SELECT
 a.empid,
 a.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 <= a.ordermonth
WHERE DATE_FORMAT(a.ordermonth,'%Y')='2015' AND DATE_FORMAT(b.ordermonth,'%Y')='2015'
GROUP BY a.empid,a.ordermonth,a.qty
HAVING total-a.qty < 1000 AND total >= 1000
ORDER BY a.empid,a.ordermonth

運(yùn)行結(jié)果如下