MySQL-with|MySQL-with rollup函数运用 _20160930 MySQL-withrollup函数运用_20160930

在博客里http://www.cnblogs.com/Mr-Cxy/p/5898839.html提到了行转列，
如果想在下面这个表下面添加一行总计数据行SQL代码怎么实现并且根据9月金额进行城市降序总计置于底部呢
MySQL提供了 group by with rollup 函数进行group by 字段的汇总
但是order by 互斥的不能同时用

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【MySQL-with|MySQL-with rollup函数运用 _20160930】第一步还是是先计算各城市每个月的金额

SELECT b.城市,SUM(IF(b.年月=201607,b.金额,NULL)) AS 7月金额,SUM(IF(b.年月=201608,b.金额,NULL)) AS 8月金额,SUM(IF(b.年月=201609,b.金额,NULL)) AS 9月金额 FROM ( SELECT city AS 城市,DATE_FORMAT(order_time,"%Y%m") AS 年月,SUM(pay_money) AS 金额 FROM test_a03order AS a GROUP BY city,DATE_FORMAT(order_time,"%Y%m") ) AS b GROUP BY b.城市

MySQL-with|MySQL-with rollup函数运用 _20160930

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第二步我们先用group by with rollup 函数添加针对字段的汇总

SELECT b.城市,SUM(IF(b.年月=201607,b.金额,NULL)) AS 7月金额,SUM(IF(b.年月=201608,b.金额,NULL)) AS 8月金额,SUM(IF(b.年月=201609,b.金额,NULL)) AS 9月金额 FROM ( SELECT city AS 城市,DATE_FORMAT(order_time,"%Y%m") AS 年月,SUM(pay_money) AS 金额 FROM test_a03order AS a GROUP BY city,DATE_FORMAT(order_time,"%Y%m") ) AS b GROUP BY b.城市 WITH ROLLUP

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这个记录没有出现总计两个字，怎么实现呢继续修改代码 ifnull()函数
第三添加总计字样(有坑) ifnull()函数是将空字段另外命名

SELECT IFNULL(b.城市,"总计") AS 城市,SUM(IF(b.年月=201607,b.金额,NULL)) AS 7月金额,SUM(IF(b.年月=201608,b.金额,NULL)) AS 8月金额,SUM(IF(b.年月=201609,b.金额,NULL)) AS 9月金额 FROM ( SELECT city AS 城市,DATE_FORMAT(order_time,"%Y%m") AS 年月,SUM(pay_money) AS 金额 FROM test_a03order AS a GROUP BY city,DATE_FORMAT(order_time,"%Y%m") ) AS b GROUP BY b.城市 WITH ROLLUP

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第四摆脱掉坑
为什么说有坑呢如果ifnull()函数放在上面代码位置看似实现了总计的字样ifnull()是针对用了with rollup 函数总计这个位置出现空字段时候修改它为总计字样的,
如果城市这一列里本身就含有没有命名的城市呢这一列就会出现多个总计字样因此我们需要将ifnull()函数放到嵌套的子表里将空字段在子表里面就预先改成别名（不能是总计字样）
因此使用2个ifnull()函数就不会有这样的问题结果是一样的

SELECT IFNULL(b.城市,"总计") AS 城市,SUM(IF(b.年月=201607,b.金额,NULL)) AS 7月金额,SUM(IF(b.年月=201608,b.金额,NULL)) AS 8月金额,SUM(IF(b.年月=201609,b.金额,NULL)) AS 9月金额 FROM ( SELECT IFNULL(city,'空城市') AS 城市,DATE_FORMAT(order_time,"%Y%m") AS 年月,SUM(pay_money) AS 金额 FROM test_a03order AS a GROUP BY city,DATE_FORMAT(order_time,"%Y%m") ) AS b GROUP BY b.城市 WITH ROLLUP

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第五排序
在这篇博客http://www.cnblogs.com/Mr-Cxy/p/5910291.html 提到了order by field()自定义排序函数如下图红框所示有这样一个默认的自定义排序规则

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因此如果想实现根据9月金额进行城市降序总计置于底部效果可以把上面代码当成一个子表嵌套结合 order by field()自定义函数实现

SELECT c.* FROM ( SELECT IFNULL(b.城市,"总计") AS 城市,SUM(IF(b.年月=201607,b.金额,NULL)) AS 7月金额,SUM(IF(b.年月=201608,b.金额,NULL)) AS 8月金额,SUM(IF(b.年月=201609,b.金额,NULL)) AS 9月金额 FROM ( SELECT IFNULL(city,'空城市') AS 城市,DATE_FORMAT(order_time,"%Y%m") AS 年月,SUM(pay_money) AS 金额 FROM test_a03order AS a GROUP BY city,DATE_FORMAT(order_time,"%Y%m") ) AS b GROUP BY b.城市 WITH ROLLUP ) AS c ORDER BY FIELD(城市,'总计'),c.9月金额 DESC