Sql server 基于最新时间戳的SQL Server表groupby日期和值

考虑下面的表1和表2，以及预期产出的预期结果

所需输出

我的目标是根据最新的

p_日期

（本例为2020-05-31）筛选所有条目，然后在

id

和

mon_year

上选择

groupby

，但仅根据时间戳选择最新条目

最后，将两个表连接起来，并为on和其他表中未找到的值分配

NULL

（参见第4行）

先谢谢你

这是针对SQL Server 2012的

-- table 1 spent values, desired values commented 
create table spent
(
    id bigint, 
    mon_year varchar(100), 
    p_date date, 
    timestamp datetime, 
    spent decimal(9,2)
);

insert into spent 
values (12345, 'Oct-20', '2020-05-31', '2020-06-18 12:16:56', 100.0), --1
       (12345, 'Oct-20', '2020-05-31', '2020-06-18 12:11:56', 150.0),
       (12345, 'Nov-20', '2020-05-31', '2020-06-18 12:10:56', 250.0), --2
       (12345, 'Mar-20', '2020-05-31', '2020-06-18 12:15:56', 10.0),  --3
       (12345, 'Jan-20', '2020-05-31', '2020-06-18 12:13:56', 5.0), --4
       (12345, 'Mar-20', '2020-05-31', '2020-06-18 12:12:56', 0.0),
       (12345, 'Oct-20', '2020-04-30', '2020-05-15 08:16:56', 1000.0),
       (12300, 'Mar-20', '2020-04-30', '2020-06-19 12:11:56', 150.0),
       (12300, 'Nov-20', '2020-05-31', '2020-06-19 12:10:56', 250.0), --5
       (12300, 'Mar-20', '2020-05-31', '2020-06-18 12:15:56', 10.0), --6
       (12300, 'Mar-20', '2020-05-31', '2020-06-18 12:12:56', 0.0);

-- table 2 forecast values, desired values commented 
create table forecast
(
    id bigint, 
    mon_year varchar(100), 
    p_date date, 
    timestamp datetime, 
    forecast decimal(9,2)
);

insert into forecast values
(12345, 'Oct-20', '2020-05-31', '2020-06-18 12:16:56',50.0 ), --1
(12345, 'Oct-20', '2020-05-31', '2020-06-18 12:11:56', 100.0), 
(12345, 'Nov-20', '2020-05-31', '2020-06-18 12:10:56',30.0 ), --2
(12345, 'Mar-20', '2020-05-31', '2020-06-18 12:15:56',40.0 ), --3
(12345, 'Mar-20', '2020-05-31', '2020-06-18 12:12:56', 0.0),
(12345, 'Oct-20', '2020-04-30', '2020-05-15 08:16:56', 0.0), 
(12300, 'Mar-20', '2020-04-30', '2020-06-19 12:11:56', 100.0), 
(12300, 'Nov-20', '2020-05-31', '2020-06-19 12:10:56',200.0 ), --5
(12300, 'Mar-20', '2020-05-31', '2020-06-18 12:15:56', 100.0), --6
(12300, 'Mar-20', '2020-05-31', '2020-06-18 12:12:56', 0.0);

-- desired final table join, values 
create table desired_outcome
(
    id bigint, 
    mon_year varchar(100), 
    p_date date, 
    forecast decimal(9,2), 
    spent decimal(9,2)
);

insert into desired_outcome values
(12345, 'Oct-20', '2020-05-31', 50.0, 100.0 ), --1
(12345, 'Nov-20', '2020-05-31', 30.0, 250.0 ), --2
(12345, 'Mar-20', '2020-05-31', 40.0, 10.0 ), --3
(12345, 'Jan-20', '2020-05-31', NULL, 5.0 ), --4
(12300, 'Nov-20', '2020-05-31', 200.0, 250.0), --5
(12300, 'Mar-20', '2020-05-31', 100.0, 10.0); --6

---

下面的代码运行到公共表表达式，以使用

行号（）

窗口函数获得每个

周一年
\
id
组合的最新时间戳记录，然后使用
完全联接
将它们组合在一起。
full join
允许存在支出或预测。要从两个表中获取最新日期，请事先运行一个变量以获取最大日期。注释代码如下：

-- Get the maximum date available from either table
declare @max_date date = (
    select
    max(p_date)
    from (
    select distinct
    p_date
    from spent

    union

    select distinct
    p_date
    from forecast
    ) as x
);



with latest_spend as (
        select
        id
        ,mon_year
        ,p_date
        ,spent
        -- The partition by is the grouping you asked for, the order by is to get the latest, and this ranks them newest to oldest
        ,row_number() over (partition by mon_year, id order by [timestamp] desc) as row_no
        from spent
        where p_date = @max_date
    
    )
    , 
    latest_forecast as (
    
    select
        id
        ,mon_year
        ,p_date
        ,forecast
        -- The partition by is the grouping you asked for, the order by is to get the latest, and this ranks them newest to oldest as  the first cte.
        ,row_number() over (partition by mon_year, id order by [timestamp] desc) as row_no
        from forecast
        where p_date = @max_date
    )
    select
        ls.id
        ,ls.mon_year
        ,ls.p_date
        ,lf.forecast
        ,ls.spent
    from latest_spend as ls
    full join latest_forecast as lf on ls.mon_year = lf.mon_year 
        and ls.id = lf.id
        and lf.row_no = 1 -- full join,  so either a spend or a forecast can be present.
    where ls.row_no =1
    order by id desc, mon_year asc;

到目前为止，您尝试了什么，为什么不起作用？我尝试按id和p_日期分组，并应用where子句，其中p_日期等于最大值（p_日期）；我遇到了一些问题，在datetime部分，甚至在我陈述逻辑的顺序上都有不足之处。有什么想法吗？谢谢！！如何将
p_date
添加到脚本中，使其始终默认为提供的最新最大值，而不是将其（即“2020-05-31”）编码到脚本中？我已对答案进行了修改，以适应这一情况，使用一个变量来评估两个表中的最大日期。