即使select中没有结果，也会显示日期范围内的所有月份

Question

我有以下查询，日期范围介于＆＃39; 09/01/16 ＆＃39;和＆＃39; 12/30/16 ＆＃39;。在附图中，结果仅适用于 9月和 10月，我仍希望显示 11月和 12月（或计数 0

的给定date2范围

我该如何做到这一点？

declare @date1 date = '09/01/16'
declare @date2 date = '12/30/16'

select 
    count(distinct w.wkid) as WksCount
    ,DATENAME(MONTH, r.date) as [month]
    ,year(r.date) as [year]
from
    Workshop w
    left join Reservation r on r.wkid=w.wkid
    left join Registration reg on reg.wkid=w.wkid
where
    r.date between @date1 and @date2
group by
    DatePart(Month, r.date)
    ,DateName(Month, r.date)
    ,year(r.date)
order by
    year(r.date)
    ,DatePart(Month, r.date)

我

Answer 1

稍微不同 - 我认为更容易理解和理解 - 方法，您可以使用CTE构建您的日期表并从中加入以获取完整的月份列表。

我已在cte中指定了月初和月末，因此您可以join从on开始，而无需使用r.date条件中的功能如果您的Workshop表很大，则会触发，因为这些函数会禁止索引利用。

如果您的datetime字段为declare @date1 date = '20160801'; declare @date2 date = '20161231'; with Dates as ( select dateadd(m,datediff(m,0,@date1),0) as MonthStart ,dateadd(d,-1,dateadd(m,datediff(m,0,@date1)+1,0)) as MonthEnd union all select dateadd(m,1,MonthStart) ,dateadd(d,-1,dateadd(m,2,MonthStart)) from Dates where MonthStart < dateadd(m,datediff(m,0,@date2),0) ) select count(distinct w.wkid) as WksCount ,DATENAME(MONTH, d.MonthStart) as [month] ,year(d.MonthStart) as [year] from Dates d left join Reservation r on r.date between d.MonthStart and d.MonthEnd and r.date between @date1 and @date2 left join Workshop w on r.wkid=w.wkid left join Registration reg on reg.wkid=w.wkid group by DatePart(Month, r.date) ,DateName(Month, r.date) ,year(r.date) order by year(r.date) ,DatePart(Month, r.date); ，则需要调整以下值以处理该月最后一天的最后一毫秒的值：

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Answer 2

这是Sean Lange所建议的主旨。

1：首先构建tally table。

2：然后，计数表与左连接一起使用以获取日期之间的所有月份，并且您将数据链接到正确的月份。 （最小值和最大值包含在我的代码示例中）

因此，没有数据的月份除了月份数之外，每列中只有一条记录为空。 现在要使用月份名称而不是月份编号，请参阅this question以了解具体方法。

P.S：月份数是Tally.N

declare @date1 date = '09/01/16'
declare @date2 date = '12/30/16'

--1: Build a tally table with CTE
;WITH
N0(_)            AS (SELECT NULL UNION ALL SELECT NULL),
N1(_)            AS (SELECT NULL FROM N0 AS L CROSS JOIN N0 AS R),
Tally            AS (SELECT N = ROW_NUMBER() OVER (ORDER BY (SELECT NULL))  FROM N1 AS L CROSS JOIN N1 AS R)

--2: Select data using the tally
select 
    count(distinct w.wkid) as WksCount
    ,Tally.N as [monthNo]
from Tally,
LEFT JOIN Reservation   AS r    ON Tally.N = DATEPART(MONTH, r.date)
                                AND r.date >= @date1
                                AND r.daye <= @date2
LEFT JOIN Workshop      AS w    ON r.wkid = w.wkid
left join Registration  AS reg  ON w.wkid = reg.wkid
WHERE Tally.N >= DATEPART(MONTH, @date1)
AND  Tally.N <= DATEPART(MONTH, @date2)
GROUP BY
    Tally.N --N is the month number
ORDER BY
    Tally.N

Answer 3

对于使用表变量作为“基表”的非常大的结果表来说更容易：

--add these lines before your select
declare @d datetime set @d=@date1
declare @t table(count int, month varchar(12), year int)
--fill the table with 0-month-year values
while @d < @date2
begin
    insert into @t values(0, datename(mm, @d), datepart(yy, @d))
    set @d = dateadd(mm, 1, @d)
end

然后将结果添加到表变量：

insert into @t 
select count(distinct w.wkid)
    ,DATENAME(MONTH, r.date)
    ,year(r.date)
from Workshop w
    left join Reservation r on r.wkid=w.wkid
    left join Registration reg on reg.wkid=w.wkid
where r.date between @date1 and @date2
group by DatePart(Month, r.date) ,DateName(Month, r.date), year(r.date)

最后获得所需的结果：

select sum(count) as count, month, year from @t
    group by year, month
    order by year desc, month desc 

来自相对较少的表变量的聚合查询比另一个LEFT JOIN便宜得多。如果你有很多句号，可以考虑使用#temporary table。

抱歉，我现在没有安装MSSqlServer来检查我的代码，但这个想法非常简单。