Mysql视图，其中根据日期将值划分为多行

Question

MySql版本：5.6.47

假设我有一个这样的表：

[from:Datetime][to:Datetime][amount:Decimal(10,2)]
[2020/01/15   ][2020/02/15 ][300                 ]

我想从中创建这样的视图：

[period:char(7)][amount:Decimal(10,2)]
[2020/01       ][150                 ]
[2020/02       ][150                 ]

起始日期和截止日期在单个月份中分开。该金额乘以该特定月份中从天到天之间的总天数的天数。从和到可能跨越n个月的时间。

甚至有可能还是我在浪费时间研究这个问题？

Answer 1

假设范围内的月数不超过100：

SELECT id,
       datefrom,
       datetill,
       amount,
       monthstart,
       monthfinish,
       amount * (DATEDIFF(LEAST(datetill, monthfinish), GREATEST(datefrom, monthstart)) + 1) / (DATEDIFF(datetill, datefrom) + 1) monthamount
FROM ( SELECT test.*,
              test.datefrom + INTERVAL numbers.num MONTH - INTERVAL DAY(test.datefrom) - 1 DAY monthstart,
              test.datefrom + INTERVAL numbers.num + 1 MONTH - INTERVAL DAY(test.datefrom) DAY monthfinish
       FROM test
       JOIN ( SELECT t1.num*10+t2.num num
              FROM (SELECT 0 num UNION SELECT 1 UNION SELECT 2 UNION SELECT 3 UNION SELECT 4 UNION SELECT 5 UNION SELECT 6 UNION SELECT 7 UNION SELECT 8 UNION SELECT 9) t1
              JOIN (SELECT 0 num UNION SELECT 1 UNION SELECT 2 UNION SELECT 3 UNION SELECT 4 UNION SELECT 5 UNION SELECT 6 UNION SELECT 7 UNION SELECT 8 UNION SELECT 9) t2
            ) numbers
       HAVING monthstart <= test.datetill
          AND monthfinish >= test.datefrom
     ) subquery
ORDER BY id, monthstart;

fiddle

PS。如果总金额与最后一位数字不匹配，请不要感到惊讶。