mysql累积聚合原理与用法实例分析

本文实例讲述了mysql累积聚合原理与用法。分享给大家供大家参考，具体如下：

累积聚合为聚合从序列内第一个元素到当前元素的数据，如为每个员工返回每月开始到现在累积的订单数量和平均订单数量

行号问题有两个解决方案，分别是为使用子查询和使用连接。子查询的方法通常比较直观，可读性强。但是在要求进行聚合时，子查询需要为每个聚合扫描一次数据，而连接方法通常只需要扫描一次就可以得到结果。下面的查询使用连接来得到结果

SELECT a.empid, a.ordermonth,a.qty AS thismonth, SUM(b.qty) AS total, CAST(AVG(b.qty) AS DECIMAL(5,2)) AS avgFROM emporders aINNER JOIN emporders b  ON a.empid=b.empid  AND b.ordermonth <= a.ordermonthGROUP BY a.empid,a.ordermonth,a.qtyORDER BY a.empid,a.ordermonth

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

此外可能还需要筛选数据，例如只需要返回每个员工到达某一目标之前每月订单的情况。这里假设统计每个员工的合计订单数量达到1000之前的累积情况。

这里可以使用HAVING过滤器来完成查询

SELECT a.empid, a.ordermonth,a.qty AS thismonth, SUM(b.qty) AS total, CAST(AVG(b.qty) AS DECIMAL(5,2)) AS avgFROM emporders aINNER JOIN emporders b  ON a.empid=b.empid  AND b.ordermonth <= a.ordermonthWHERE DATE_FORMAT(a.ordermonth,'%Y')='2015' AND DATE_FORMAT(b.ordermonth,'%Y')='2015'GROUP BY a.empid,a.ordermonth,a.qtyHAVING total<1000ORDER BY a.empid,a.ordermonth

SELECT a.empid, a.ordermonth,a.qty AS thismonth, SUM(b.qty) AS total, CAST(AVG(b.qty) AS DECIMAL(5,2)) AS avgFROM emporders aINNER JOIN emporders b  ON a.empid=b.empid  AND b.ordermonth <= a.ordermonthWHERE DATE_FORMAT(a.ordermonth,'%Y')='2015' AND DATE_FORMAT(b.ordermonth,'%Y')='2015'GROUP BY a.empid,a.ordermonth,a.qtyHAVING total-a.qty < 1000ORDER BY a.empid,a.ordermonth

如果只想返回达到累积订单数为1000的当月数据，不返回之前的月份，则可以对上述SQL语句

进一步过滤，再添加累积订单数量大于等于1000的条件。该问题的SQL语句如下，

SELECT a.empid, a.ordermonth,a.qty AS thismonth, SUM(b.qty) AS total, CAST(AVG(b.qty) AS DECIMAL(5,2)) AS avgFROM emporders aINNER JOIN emporders b  ON a.empid=b.empid  AND b.ordermonth <= a.ordermonthWHERE DATE_FORMAT(a.ordermonth,'%Y')='2015' AND DATE_FORMAT(b.ordermonth,'%Y')='2015'GROUP BY a.empid,a.ordermonth,a.qtyHAVING total-a.qty < 1000 AND total >= 1000ORDER BY a.empid,a.ordermonth

更多关于MySQL相关内容感兴趣的读者可查看本站专题：《MySQL查询技巧大全》、《MySQL常用函数大汇总》、《MySQL日志操作技巧大全》、《MySQL事务操作技巧汇总》、《MySQL存储过程技巧大全》及《MySQL数据库锁相关技巧汇总》

希望本文所述对大家MySQL数据库计有所帮助。

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