Question

刚刚意识到我的SQL命令无法正常工作。

基本上我有一个有两列的表。它记录每个月的用户数。布局是这样的：

StatDate    UserCount
--------    ---------
11/2/2012       5
12/8/2012      10
12/23/2012     25
1/8/2013       50
2/18/2013      100
3/22/2013      33

等等。您可以看到每月可以有多个条目。我需要能够检索过去一年中每个月的最新值，以便将其放在折线图中。

我这样做：

SELECT TOP 1 UserCount FROM Stats_UserCount WHERE MONTH(StatDate)=MONTH(GetDate()) - 0 ORDER BY StatDate DESC;
SELECT TOP 1 UserCount FROM Stats_UserCount WHERE MONTH(StatDate)=MONTH(GetDate()) - 1 ORDER BY StatDate DESC;
SELECT TOP 1 UserCount FROM Stats_UserCount WHERE MONTH(StatDate)=MONTH(GetDate()) - 2 ORDER BY StatDate DESC;
SELECT TOP 1 UserCount FROM Stats_UserCount WHERE MONTH(StatDate)=MONTH(GetDate()) - 3 ORDER BY StatDate DESC;
SELECT TOP 1 UserCount FROM Stats_UserCount WHERE MONTH(StatDate)=MONTH(GetDate()) - 4 ORDER BY StatDate DESC;
SELECT TOP 1 UserCount FROM Stats_UserCount WHERE MONTH(StatDate)=MONTH(GetDate()) - 5 ORDER BY StatDate DESC;
SELECT TOP 1 UserCount FROM Stats_UserCount WHERE MONTH(StatDate)=MONTH(GetDate()) - 6 ORDER BY StatDate DESC;
SELECT TOP 1 UserCount FROM Stats_UserCount WHERE MONTH(StatDate)=MONTH(GetDate()) - 7 ORDER BY StatDate DESC;
SELECT TOP 1 UserCount FROM Stats_UserCount WHERE MONTH(StatDate)=MONTH(GetDate()) - 8 ORDER BY StatDate DESC;
SELECT TOP 1 UserCount FROM Stats_UserCount WHERE MONTH(StatDate)=MONTH(GetDate()) - 9 ORDER BY StatDate DESC;
SELECT TOP 1 UserCount FROM Stats_UserCount WHERE MONTH(StatDate)=MONTH(GetDate()) - 10 ORDER BY StatDate DESC;
SELECT TOP 1 UserCount FROM Stats_UserCount WHERE MONTH(StatDate)=MONTH(GetDate()) - 11 ORDER BY StatDate DESC;

但是，当MONTH为负数时，您可以看到问题出现，因为它不知道如何去往前一年。有没有更好的方法来实现这个目标？

Answer 1

假设您正在使用SQL Server 。

您可以通过将StatDate与上一年当前月份的第一个数字进行比较来获得过去12个月:) StatDate >= dateadd(month, datediff(month, 0, getdate()) - 12, 0);（如果您有任何问题，此类查询也将使用StatDate列上的索引）。您可以使用row_number()函数在一个查询中获取所需的数据：

with cte as (  
    select
        StatDate, UserCount,
        row_number() over(partition by month(StartDate) order by StartDate desc) as rn
    from Table1
    where StatDate >= dateadd(month, datediff(month, 0, getdate()) - 12, 0)
)
select StatDate, UserCount
from Table1
where rn = 1

<强> sql fiddle demo

Answer 2

使用派生表获取过去一年中每个月的最新日期，然后使用原始表进行内部联接，以获得这些日期所需的计数：

SELECT UserCount, T.STATDATE
FROM 
    (SELECT MAX(StatDate) AS STATDATE
     FROM STATS_USERCOUNT
     WHERE DATEDIFF(MONTH,GETDATE(),StatDate) <=12
     GROUP BY MONTH(StatDate)) AS T
INNER JOIN STATS_USERCOUNT S ON T.STATDATE = S.StatDate ;

SQL获取过去12个月的数据

2 个答案: