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過濾器來完成查詢
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 total1000
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)問題的過濾,可以從另外一個(gè)方面來考慮。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1000的月份進(jìn)行統(tǒng)計(jì)。故該解決方案的SQL語句如下
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語句
進(jìn)一步過濾,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
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希望本文所述對(duì)大家MySQL數(shù)據(jù)庫(kù)計(jì)有所幫助。
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