Question

我需要一个关于MySQL的最后两个条目之间的区别的解决方案

SELECT DATE_FORMAT(order_datetime,'%m/%Y') as date,
       SUM(order_total_after_tax) as number
FROM tbl_order 
WHERE status = 'Confirmed'
GROUP BY DATE_FORMAT(order_datetime,'%Y/%m')
Limit 2

输出：

date     number
02/2019 2345.01
03/2019 103751.05

但是我需要一个精确的解决方案，就是我需要找到最后2个结果之间的差异

2345.01 -103751.05

结果：-101406.04 在MySQL中怎么做？查询是什么？

Answer 1

您可以尝试交叉加入

select   a.date, a.number, b.number, a.number - b.number my_diff
from (

  SELECT DATE_FORMAT(order_datetime,'%m/%Y') as date
    , SUM(order_total_after_tax) as number 
  FROM tbl_order 
  where status='Confirmed' 
  GROUP BY DATE_FORMAT(order_datetime,'%Y/%m') 
  Limit 2
)  a 
CROSS JOIN (
  SELECT DATE_FORMAT(order_datetime,'%m/%Y') as date
    , SUM(order_total_after_tax) as number 
  FROM tbl_order 
  where status='Confirmed' 
 GROUP BY DATE_FORMAT(order_datetime,'%Y/%m') 
) b ON a.date = b.date and a.number <> b.number

Answer 2

一种方法是cross join，但它看起来像这样：

SELECT last.number - last_1.number
FROM (SELECT DATE_FORMAT(order_datetime,'%m/%Y') as date,
             SUM(order_total_after_tax) as number
      FROM tbl_order 
      WHERE status = 'Confirmed'
      GROUP BY DATE_FORMAT(order_datetime,'%Y/%m')
      ORDER BY date
      LIMIT 1
     ) as last CROSS JOIN
     (SELECT DATE_FORMAT(order_datetime,'%m/%Y') as date,
             SUM(order_total_after_tax) as number
      FROM tbl_order 
      WHERE status = 'Confirmed'
      GROUP BY DATE_FORMAT(order_datetime,'%Y/%m')
      ORDER BY date
      LIMIT 1 OFFSET 1
     ) last_1

Answer 3

SELECT last.number - last_1.number FROM (SELECT DATE_FORMAT(order_datetime,'%m/%Y') as date, SUM(order_total_after_tax) as number FROM tbl_order WHERE status = 'Confirmed' GROUP BY DATE_FORMAT(order_datetime,'%Y/%m') ORDER BY date DESC LIMIT 1 ) as last CROSS JOIN (SELECT DATE_FORMAT(order_datetime,'%m/%Y') as date, SUM(order_total_after_tax) as number FROM tbl_order WHERE status = 'Confirmed' GROUP BY DATE_FORMAT(order_datetime,'%Y/%m') ORDER BY date DESC LIMIT 1 OFFSET 1 ) last_1

如何找到Mysql中最后两个条目之间的区别

3 个答案: