如果在日期期间没有可用的行，则SQL Server分组的行将返回默认值

Question

我正在尝试编写一个存储过程，该存储过程根据行的月份对行进行分组，如果存在则返回所有项的总和，如果不存在则返回0。

对于查询的日期部分，我要获取的是今天的日期-提取月份，然后返回5个月以收集所有数据（如果存在）。

在此阶段，查询按原样运行良好，但是我想知道是否有任何方法可以对此进行优化，因为我好像一次又一次地运行同一组数据，并且在一定程度上进行了硬编码。

我试图实现的数据集如下：

Month    TotalAmount    TotalCount
-----------------------------------
2017-11  0              0
2017-12  200.00         2
2018-01  300.00         3
2018-02  0              0
2018-03  300.00         3
2018-04  100.00         1

使用下面的以下查询，我可以实现所需的功能，但是如您所见，过去5个月很难进行编码，因此，如果我想回到12个月，则必须添加更多代码。

DECLARE @5MonthAgo date = CAST(DATEADD(MONTH, -5, GETDATE()) + 1 - DATEPART(DAY, DATEADD(MONTH, -5, GETDATE())) AS DATE)
DECLARE @4MonthAgo date = CAST(DATEADD(MONTH, -4, GETDATE()) + 1 - DATEPART(DAY, DATEADD(MONTH, -4, GETDATE())) AS DATE)
DECLARE @3MonthAgo date = CAST(DATEADD(MONTH, -3, GETDATE()) + 1 - DATEPART(DAY, DATEADD(MONTH, -3, GETDATE())) AS DATE)
DECLARE @2MonthAgo date = CAST(DATEADD(MONTH, -2, GETDATE()) + 1 - DATEPART(DAY, DATEADD(MONTH, -2, GETDATE())) AS DATE)
DECLARE @1MonthAgo date = CAST(DATEADD(MONTH, -1, GETDATE()) + 1 - DATEPART(DAY, DATEADD(MONTH, -1, GETDATE())) AS DATE)
DECLARE @CurrentMonth date = CAST(GETDATE() + 1 - DATEPART(DAY, GETDATE()) AS DATE)

-- Table to return grouped and sum data
DECLARE @StatsTable TABLE ([Month] DATE, 
                           [Total Amount] DECIMAL(18,2),
                           [Total Count] INT
                          )

-- Temporary table to hold onto data batch - so table isn't used later on
DECLARE @TempGenTable TABLE ([Id] INT,
                             [Date] DATETIME,
                             [Lines] INT NULL,
                             [Amount] DECIMAL(18, 2) NULL
                            )

INSERT INTO @TempGenTable
    SELECT
        Id, Date, Lines, Amount
    FROM 
        TallyTable
    WHERE 
        Date >= @5MonthAgo

INSERT INTO @StatsTable
    SELECT
        @5MonthAgo,
        COALESCE((SELECT SUM(Amount)
                  FROM @TempGenTable
                  WHERE Date >= @5MonthAgo AND Date < @4MonthAgo
                  GROUP BY DATEADD(MONTH, DATEDIFF(MONTH, 0, Date), 0)), 0),
        COALESCE((SELECT COUNT(Id)
                  FROM @TempGenTable
                  WHERE Date >= @5MonthAgo AND Date < @4MonthAgo
                  GROUP BY DATEADD(MONTH, DATEDIFF(MONTH, 0, Date), 0)), 0)

    UNION

    SELECT
        @4MonthAgo,
        COALESCE((SELECT SUM(Amount)
                  FROM @TempGenTable
                  WHERE Date >= @4MonthAgo AND Date < @3MonthAgo
                  GROUP BY DATEADD(MONTH, DATEDIFF(MONTH, 0, Date), 0)), 0),
        COALESCE((SELECT COUNT(Id)
                  FROM @TempGenTable
                  WHERE Date >= @4MonthAgo AND Date < @3MonthAgo
                  GROUP BY DATEADD(MONTH, DATEDIFF(MONTH, 0, Date), 0)), 0)
     ...

有没有更简单的方法可以在几个月内获得更多灵活性的上述数据？

只是让查询传递一个month变量并只检查当前月份并在控制器内循环以返回x个月，这更好吗？

Answer 1

我将使用递归CTE生成数据，然后使用left join ：

with months as (
      select datefromparts(year(getdate()), month(getdate()), 1) as month_start, 5 as n
      union all
      select dateadd(month, -1, month_start), n - 1
      from months
      where n > 0
     )
select m.month_start, count(s.id), sum(s.amount)
from months m left join
     @StatsTable s
     on m.month_start = s.month
group by m.month_start
order by m.month_start;

您尚未提供示例数据，所以我不确定s.month是什么样。 您可能希望加入条件为：

on s.month >= m.month_start and s.month < dateadd(month, 1, m.month_start)

Answer 2

以下是一种基于集合的方法来生成所需的月度周期：

--sample data
CREATE TABLE dbo.TallyTable (
      Id int
    , Date datetime
    , Lines int 
    , Amount decimal(18, 2)
    );
INSERT INTO dbo.TallyTable
VALUES
     (1, '2017-12-05', 1, 50.00)
    ,(2, '2017-12-06', 1, 150.00)
    ,(3, '2018-01-10', 1, 100.00)
    ,(4, '2018-01-11', 1, 100.00)
    ,(5, '2018-01-12', 1, 100.00)
    ,(6, '2018-03-15', 1, 225.00)
    ,(7, '2018-03-15', 1, 25.00)
    ,(8, '2018-03-15', 1, 50.00)
    ,(9, '2018-04-20', 1, 100.00);
GO

DECLARE @Months int = 5; --number of historical months
WITH
     t10 AS (SELECT n FROM (VALUES(0),(0),(0),(0),(0),(0),(0),(0),(0),(0)) t(n))
    ,t100 AS (SELECT ROW_NUMBER() OVER (ORDER BY (SELECT 0)) - 1 AS num FROM t10 AS a CROSS JOIN t10 AS b)
    , periods AS (SELECT
              CONVERT(varchar(7), DATEADD(month, DATEDIFF(month, '', GETDATE()) - num, ''),121) AS Month
            , DATEADD(month, DATEDIFF(month, '', CAST(GETDATE() AS date)) - num, '') AS PeriodStart
            , DATEADD(month, DATEDIFF(month, '', CAST(GETDATE() AS date)) - num + 1, '') AS NextPeriodStart
        FROM t100
        WHERE num <= @Months
    )
SELECT periods.Month, COALESCE(SUM(Amount), 0) AS TotalAmount, COALESCE(COUNT(ID), 0) AS TotalCount
FROM periods
LEFT JOIN dbo.TallyTable ON
    TallyTable.Date >= PeriodStart
    AND TallyTable.Date < NextPeriodStart
GROUP BY periods.Month
ORDER BY periods.Month;