为持久化计算列简化 T-SQL 用户函数

Question

我正在尝试简化以下 T-SQL 用户函数，以便在我的一个表的持久计算列中使用。我知道我可以在视图中使用计算列以及其他方法，但由于用户要求的各种原因，最好这样实现此列。

但是，为了在计算机专栏中使用此标量函数，我正在尝试使其尽可能高效和流线型。该函数的某些部分带有以下SELECT COUNT 语句

SELECT COUNT([JunctionID])
FROM dbo.ApplicationJunctionT
WHERE [AccountID] = @AccountID 
  AND [Outcome] IS NULL 
  AND [Change Account Status] IS NULL

我反复使用，我想知道是否有更好的方法来重组此功能以提高效率。我确实尝试使用 CTE 来包装这个 select 语句，但不断遇到语法问题，因此放弃了这个想法。

ALTER FUNCTION [dbo].[fnAccountReadyByID_Test] 
    (@JunctID INT = Null,
     @AccountID VARCHAR(20) = NULL)
RETURNS VARCHAR(10)
AS
BEGIN
    DECLARE @FamilyAccountReady as varchar(10),
            @TotalFamily as INT;

    SET @TotalFamily = (SELECT COUNT([JunctionID])
                        FROM dbo.ApplicationJunctionT
                        WHERE [AccountID] = @AccountID 
                          AND [Outcome] IS NULL 
                          AND [Change Account Status] IS NULL)

    IF @TotalFamily = 1
        SET @FamilyAccountReady = (SELECT AccountStatus 
                                   FROM dbo.ApplicationJunctionT 
                                   WHERE JunctionID = @JunctID)
    ELSE
        SET @FamilyAccountReady = (CASE 
                                      WHEN (SELECT COUNT([JunctionID]) 
                                            FROM dbo.ApplicationJunctionT 
                                            WHERE [AccountID] = @AccountID 
                                              AND [Outcome] IS NULL 
                                              AND [Change Account Status] IS NULL 
                                              AND [AccountStatus] = '-') > 0 
                                         THEN '-'
                                      WHEN (SELECT COUNT([JunctionID]) 
                                            FROM dbo.ApplicationJunctionT 
                                            WHERE [AccountID] = @AccountID 
                                              AND [Outcome] IS NULL 
                                              AND [Change Account Status] IS NULL 
                                              AND [AccountStatus] = 'Frozen') > 0 
                                         THEN 'Frozen'
                                      WHEN (SELECT COUNT([JunctionID]) 
                                            FROM dbo.ApplicationJunctionT 
                                            WHERE [AccountID] = @AccountID 
                                              AND [Outcome] IS NULL 
                                              AND [Change Account Status] IS NULL 
                                              AND [AccountStatus] = 'Closed') > 0 
                                         THEN 'Closed'
                                      WHEN (SELECT COUNT([JunctionID]) 
                                            FROM dbo.ApplicationJunctionT 
                                            WHERE [AccountID] = @AccountID 
                                              AND [Outcome] IS NULL 
                                              AND [Change Account Status] IS NULL 
                                              AND [AccountStatus] = 'Tentative') > 0 
                                         THEN 'Tentative'
                                      ELSE 'GRANT'
                               END)

       -- Return the result of the function
       RETURN UPPER(@FamilyAccountReady)
END

此外，即使在网上阅读了多篇文章后，我也无法找到计算机栏的触发方式。更新记录中的任何字段时是否触发？还是仅在变量字段更新时触发？

在这种情况下，我使用AccountID 和JunctionID 作为变量，它们都是不变的静态字段。我的计算列在这种情况下是否仍然有效？

尽管我不喜欢效率低下，但我可能不得不采用这种设计，除非这里的专家社区可以提出一些改进建议！

非常感谢您的帮助！

Answer 1

如果您想使用 CTE，请尝试以下方法：

WITH CTE AS (
    SELECT [AccountStatus]
    FROM dbo.ApplicationJunctionT 
    WHERE [AccountID] = @AccountID 
        AND [Outcome] IS NULL 
        AND [Change Account Status] IS NULL 
) 
SELECT @FamilyAccountReady = CASE 
    WHEN EXISTS (SELECT * FROM CTE WHERE [AccountStatus] = '-') THEN '-'
    WHEN EXISTS (SELECT * FROM CTE WHERE [AccountStatus] = 'Frozen') THEN 'Frozen'
    WHEN EXISTS (SELECT * FROM CTE WHERE [AccountStatus] = 'Closed') THEN 'Closed'
    WHEN EXISTS (SELECT * FROM CTE WHERE [AccountStatus] = 'Tentative') THEN 'Tentative'
    ELSE 'GRANT'
END

但是，我认为使用基于访问其他表的函数的计算列不是一个好主意：您将收到错误提示 "Computed column 'ColumnName' in table 'TableName'无法持久化，因为该列是不确定的。”