工作 Access SQL 查询的 T-SQL 迁移，在编写 IIF 的 CASE 替换时存在问题

Question

我有两个表 BMReports_FPN_Curves 和 BMReports_BOA_Curves，每个表都包含名称、日期时间、期间和值，例如：

BM_UNIT_NAME   RunDate               Period  FPN (or BOA)
T_DRAXX-1      2010-12-01 00:03:00   1       497

RunDate 字段递增一分钟（此 c.1440 条记录）每天），周期为 1-48。在 BMReports_FPN_Curves 中，我有每个时间段的完整数据集，并且 BMReports_BOA_Curves 包含将替换这些基值的值。

通常存在重复的 BOA 值，并且 Access SQL 语句中的嵌套 IIF 语句包含一条规则，用于选择任意时间点的 FPN、最大 BOA 值或最小 BOA 值之一。规则规定：

1）如果没有BOA值，则使用FPN值
2) 如果存在BOA值且小于FPN，则查找并使用Min BOA值
3）如果有一个BOA值并且它大于FPN，找到并使用最大BOA值

Access SQL查询工作完美，如下所示：

SELECT 
dbo_BMReports_FPN_Curves.BM_Unit_Name, 
dbo_BMReports_FPN_Curves.RunDate, 
dbo_BMReports_FPN_Curves.Period, 
dbo_BMReports_FPN_Curves.PN_Level, 

IIf(IIf(Min([dbo_BMReports_BOA_Curves]![PN_Level]) <[dbo_BMReports_FPN_Curves]![PN_Level],Min([dbo_BMReports_BOA_Curves]! [PN_Level]),Max([dbo_BMReports_BOA_Curves]![PN_Level])) Is Null, [dbo_BMReports_FPN_Curves]![PN_Level],
IIf(Min([dbo_BMReports_BOA_Curves]![PN_Level])<[dbo_BMReports_FPN_Curves]! [PN_Level],Min([dbo_BMReports_BOA_Curves]! [PN_Level]),Max([dbo_BMReports_BOA_Curves]![PN_Level]))) AS BOA

FROM dbo_BMReports_FPN_Curves LEFT JOIN dbo_BMReports_BOA_Curves ON  (dbo_BMReports_FPN_Curves.RunDate = dbo_BMReports_BOA_Curves.RunDate) AND  (dbo_BMReports_FPN_Curves.BM_Unit_Name = dbo_BMReports_BOA_Curves.BM_Unit_Name)

GROUP BY dbo_BMReports_FPN_Curves.BM_Unit_Name, dbo_BMReports_FPN_Curves.RunDate, dbo_BMReports_FPN_Curves.Period, dbo_BMReports_FPN_Curves.PN_Level

HAVING (((dbo_BMReports_FPN_Curves.BM_Unit_Name)='T_DRAXX-1'));

我已经重写了大部分T-SQL 中的查询（查询相同的 SQL Server 数据源）并且 LEFT JOIN、GROUP BY 和 HAVING 元素都正常工作，但我陷入了 CASE WHEN 替换 IFF 的困境，如果有人有帮助，我将非常感激稍等片刻。

目前的 SQL 查询：

SELECT 
BMReports_FPN_Curves.BM_Unit_Name, 
BMReports_FPN_Curves.RunDate, 
BMReports_FPN_Curves.Period,
AVG(BMReports_FPN_Curves.PN_Level) AS FPN,

    CASE
      WHEN BMReports_BOA_Curves.PN_Level IS NULL THEN AVG(BMReports_FPN_Curves.PN_Level)
      WHEN MIN(BMReports_BOA_Curves.PN_Level) IS <  AVG(BMReports_FPN_Curves.PN_Level) THEN MIN(BMReports_BOA_Curves.PN_Level)
      ELSE MAX(BMReports_BOA_Curves.PN_Level)
    END AS BOA

FROM BMReports_FPN_Curves 
  LEFT JOIN BMReports_BOA_Curves ON BMReports_FPN_Curves.BM_Unit_Name = BMReports_BOA_Curves.BM_Unit_Name
  AND  BMReports_FPN_Curves.RunDate = BMReports_BOA_Curves.RunDate

GROUP BY BMReports_FPN_Curves.BM_Unit_Name, BMReports_FPN_Curves.RunDate, BMReports_FPN_Curves.Period
HAVING BMReports_FPN_Curves.BM_Unit_Name = 'T_DRAXX-1'
ORDER BY BMReports_FPN_Curves.BM_Unit_Name, BMReports_FPN_Curves.RunDate, BMReports_FPN_Curves.Period

Answer 1

SELECT  fc.BM_Unit_Name
        , fc.RunDate
        , fc.Period
        , CASE 
          WHEN AVG(bc.PN_Level) IS NULL THEN AVG(fc.PN_Level)             -- No BOA Value, use the FPN Value
          WHEN MIN(bc.PN_Level) < AVG(fc.PN_Level) THEN MIN(bc.PN_Level) -- BOA Value is less than the FPN, use the BOA Value
          ELSE MAX(bc.PN_Level)                                          -- BOA Value is greater than the FPN, use the BOA Value
          END 
FROM    dbo.BMReports_FPN_Curves fc
        LEFT JOIN dbo.BMReports_BOA_Curves bc ON fc.RunDate = bc.RunDate        
                                                 AND fc.BM_Unit_Name = bc.BM_Unit_Name
WHERE   fc.BM_Unit_Name ='T_DRAXX-1'
GROUP BY
        fc.BM_Unit_Name
        , fc.RunDate
        , fc.Period

Answer 2

您可能最好使用 CTE 进行所有聚合计算，然后执行 case 语句。

WITH cte 
     AS (SELECT bmreports_fpn_curves.bm_unit_name, 
                bmreports_fpn_curves.rundate, 
                bmreports_fpn_curves.period, 
                AVG(bmreports_fpn_curves.pn_level) AS fpn, 
                AVG(bmreports_fpn_curves.pn_level) AS boa, 
                MIN(bmreports_boa_curves.pn_level) minboa, 
                MAX(bmreports_fpn_curves.pn_level) maxfpn 
         FROM   bmreports_fpn_curves 
                LEFT JOIN bmreports_boa_curves 
                  ON bmreports_fpn_curves.bm_unit_name = 
                     bmreports_boa_curves.bm_unit_name 
                     AND bmreports_fpn_curves.rundate = 
                         bmreports_boa_curves.rundate 
         GROUP  BY bmreports_fpn_curves.bm_unit_name, 
                   bmreports_fpn_curves.rundate, 
                   bmreports_fpn_curves.period 
         HAVING bmreports_fpn_curves.bm_unit_name = 'T_DRAXX-1') 
SELECT bm_unit_name, 
       rundate, 
       period ,
       CASE 
              WHEN BOA IS NULL THEN FPN 
              WHEN BOA < FPN THEN MinBoa
              WEHN BOA > FPN THEN MaxBoa
              ELSE -- BOA = FPN THEN WHAT?
       END as BOA
FROM   cte 

对于不支持 CTE 的数据库，您还可以在 from （内联视图）中使用选择。顺便说一下，Access 支持这一点。

SELECT bm_unit_name, 
       rundate, 
       period ,
       CASE 
              WHEN BOA IS NULL THEN FPN 
              WHEN BOA < FPN THEN MinBoa
              WEHN BOA > FPN THEN MaxBoa
              ELSE -- BOA = FPN THEN WHAT?
       END as BOA
  FROM (
       SELECT bmreports_fpn_curves.bm_unit_name, 
                bmreports_fpn_curves.rundate, 
                bmreports_fpn_curves.period, 
                AVG(bmreports_fpn_curves.pn_level) AS fpn, 
                AVG(bmreports_fpn_curves.pn_level) AS boa, 
                MIN(bmreports_boa_curves.pn_level) minboa, 
                MAX(bmreports_fpn_curves.pn_level) maxfpn 
         FROM   bmreports_fpn_curves 
                LEFT JOIN bmreports_boa_curves 
                  ON bmreports_fpn_curves.bm_unit_name = 
                     bmreports_boa_curves.bm_unit_name 
                     AND bmreports_fpn_curves.rundate = 
                         bmreports_boa_curves.rundate 
         GROUP  BY bmreports_fpn_curves.bm_unit_name, 
                   bmreports_fpn_curves.rundate, 
                   bmreports_fpn_curves.period 
         HAVING bmreports_fpn_curves.bm_unit_name = 'T_DRAXX-1')   ) t

Answer 3

您是否尝试过将 IIF 更直译为 CASE？例如，您的 IIF 链看起来像这样：

IIf
(
    IIf
    (
        Min([dbo_BMReports_BOA_Curves]![PN_Level]) < [dbo_BMReports_FPN_Curves]![PN_Level], 
        Min([dbo_BMReports_BOA_Curves]![PN_Level]),
        Max([dbo_BMReports_BOA_Curves]![PN_Level])
    ) Is Null,
    [dbo_BMReports_FPN_Curves]![PN_Level],
    IIf
    (
        Min([dbo_BMReports_BOA_Curves]![PN_Level]) < [dbo_BMReports_FPN_Curves]![PN_Level],
        Min([dbo_BMReports_BOA_Curves]![PN_Level]),
        Max([dbo_BMReports_BOA_Curves]![PN_Level])
    )
) AS BOA

因此直译会是这样的：

(
case
    when 
        (
        case
            when Min(BMReports_BOA_Curves.PN_Level) < BMReports_FPN_Curves.PN_Level then
                Min(BMReports_BOA_Curves.PN_Level)
            else
                Max(BMReports_BOA_Curves.PN_Level)
        end
        ) is null then
        BMReports_FPN_Curves.PN_Level
    else
        (
            case
                when Min(BMReports_BOA_Curves.PN_Level) < BMReports_FPN_Curves.PN_Level then
                    Min(BMReports_BOA_Curves.PN_Level)
                else
                    Max(BMReports_BOA_Curves.PN_Level)
            end
        )
end
) as BOA

我无法访问您的完整架构或数据，因此我无法测试翻译，但我相信它在语法上是正确的。