T-SQL CTE 自参考 CROSS APPLY 按日期有间隙的前一行

Question

我在 SQL Server 2014 中有一个更新table table 的日期值序列（比如 dbo.sequence）。日期是唯一的。

当有新的更新时，我想根据某些条件，例如如果来自 dbo.sequence 的先前值比当前 dbo.sequence 值 less/greater，它将被插入到 dbo.distributed_values 的指定列或在该列中变为 NULL。

主要思想如下：

;WITH
CTE_tbl (date, value, val_1, val_2, val_3)
AS (
SELECT ... FROM dbo.distributed_values  -- get latest values from database

UNION ALL

SELECT
   SEQ.date,
   SEQ.value,

   CASE
   WHEN ABS (SEQ.value - prev.value) >= 0.5
   THEN SEQ.value
   ELSE NULL
   END AS val_1,

   ...

   FROM dbo.sequence AS SEQ
   CROSS APPLY (SELECT * FROM CTE_tbl WHERE date = DATEADD(DAY, -1, SEQ.date)) AS prev
)

INSERT INTO dbo.distributed_values (...)
SELECT *
   FROM CTE_tbl
   ORDER BY date ASC
   OPTION (MAXRECURSION 1000)

似乎大部分都有效，但 dbo.sequence 包含间隙，因此我无法使用 date = DATEADD(DAY, -1, SEQ.date) 之类的东西正确绑定到前一行。

如何在日期间隔的情况下正确绑定以前的值？

更新：顺便说一下，我不能在 WHERE 子句中使用 LAG ... OVER，我试过了。不知何故可以在这里使用吗？

Answer 1

添加另一个 CTE 并在递归 CTE 中使用它，如下所示：

;WITH
SequenceWithPrevious AS(
    SELECT * 
        ,PrevValue = LAG(value,1,NULL) OVER (ORDER BY SEQ.date)
        ,Prevdate = LAG(date,1,NULL) OVER (ORDER BY SEQ.date)
    FROM dbo.sequence AS SEQ
),
CTE_tbl (date, value, val_1, val_2, val_3)
AS (
SELECT ... FROM dbo.distributed_values  -- get latest values from database

UNION ALL

SELECT  ...
   FROM SequenceWithPrevious AS SEQ
   CROSS APPLY (SELECT * FROM CTE_tbl WHERE date = SEQ.PrevDate) AS prev
)

INSERT INTO dbo.distributed_values (...)
SELECT *
   FROM CTE_tbl
   ORDER BY date ASC
   OPTION (MAXRECURSION 1000)

T-SQL CTE 自参考 CROSS APPLY 按日期有间隙的前一行

T-SQL CTE self-reference CROSS APPLY previous row by date with gaps

sql-server

tsql

common-table-expression

union-all