如何获得一个月中每一天的价值 [英] How to get values for every day in a month

问题描述

数据:

values date
14 1.1.2010
20 1.1.2010
10 2.1.2010
7  4.1.2010
...

有关2010年1月的示例查询应获得31行.每天一次.并应添加值.现在，我可以使用31个查询来执行此操作，但是我希望可以使用一个查询.有可能吗?

sample query about january 2010 should get 31 rows. One for every day. And values vould be added. Right now I could do this with 31 queries but I would like this to work with one. Is it possible?

结果:

1. 34
2. 10
3.  0
4.  7
...

推荐答案

这实际上在SQL中很难做到.一种方法是使用带有UNION ALL的长选择语句来生成从1到31的数字.这说明了原理，但为清楚起见，我停在4:

This is actually surprisingly difficult to do in SQL. One way to do it is to have a long select statement with UNION ALLs to generate the numbers from 1 to 31. This demonstrates the principle but I stopped at 4 for clarity:

SELECT MonthDate.Date, COALESCE(SUM(`values`), 0) AS Total
FROM (
    SELECT 1 AS Date UNION ALL
    SELECT 2 UNION ALL
    SELECT 3 UNION ALL
    SELECT 4 UNION ALL
    --
    SELECT 28 UNION ALL
    SELECT 29 UNION ALL
    SELECT 30 UNION ALL
    SELECT 31) AS MonthDate
LEFT JOIN Table1 AS T1
ON MonthDate.Date = DAY(T1.Date)
AND MONTH(T1.Date) = 1 AND YEAR(T1.Date) = 2010
WHERE MonthDate.Date <= DAY(LAST_DAY('2010-01-01'))
GROUP BY MonthDate.Date

使用表存储这些值并与其连接可能会更好.

It might be better to use a table to store these values and join with it instead.

结果:

1, 34
2, 10
3, 0
4, 7

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