Question

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

当有新的更新时，我希望在某些条件下将这些值分配到单独的表格中（例如dbo.distributed_values），例如如果dbo.sequence的先前值小于/大于当前dbo.sequence值，则会将其插入到dbo.distributed_values的指定列中，或在该列中变为NULL。

这是主要的想法：

;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)

似乎它主要起作用，但dbo.sequence包含间隙，所以我不能使用像date = DATEADD(DAY, -1, SEQ.date)这样的东西来正确绑定前一行。

如果日期空白，如何正确绑定以前的值？

UPD：顺便说一下，我试过LAG ... OVER条款中不能使用WHERE。它可以在某种程度上使用吗？

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自引用CROSS APPLY以前的行与日期有差距

1 个答案: