如何在resul中排除负值

Question

请问如何获取此查询以排除负（-）值

SELECT Enrollment.Participant_ID
    ,Enrollment.Site
    ,Enrollment.ActualDelivery
    ,Forms.[2MonthQoL]
    ,[Enrollment].[ActualDelivery] + 70 AS Due
    ,DateDiff("d", [Due], DATE ()) AS DaysOverdue
FROM Enrollment
LEFT JOIN Forms ON Enrollment.Participant_ID = Forms.Participant_IDFK
WHERE (
        ((Enrollment.ActualDelivery) IS NOT NULL)
        AND ((Forms.[2MonthQoL]) IS NULL)
        );

Answer 1

您可以将条件添加到where子句中：

WHERE Enrollment.ActualDelivery) IS NOT NULL AND
      Forms.[2MonthQoL]) IS NULL AND
      DateDiff("d", [Due], DATE()) >= 0

这自然会写成：

WHERE Enrollment.ActualDelivery) IS NOT NULL AND
      Forms.[2MonthQoL]) IS NULL AND
      [Due] <= DATE()

Answer 2

您可以使用函数ABS()来获取数字的绝对值，例如：

SELECT Enrollment.Participant_ID
    ,Enrollment.Site
    ,Enrollment.ActualDelivery
    ,Forms.[2MonthQoL]
    ,[Enrollment].[ActualDelivery] + 70 AS Due
    ,ABS(DateDiff("d", [Due], DATE ())) AS DaysOverdue
FROM Enrollment
LEFT JOIN Forms ON Enrollment.Participant_ID = Forms.Participant_IDFK
WHERE (
        ((Enrollment.ActualDelivery) IS NOT NULL)
        AND ((Forms.[2MonthQoL]) IS NULL)
        );

如果只希望这些负数为NULL，则可以使用IIF()：

SELECT Enrollment.Participant_ID
    ,Enrollment.Site
    ,Enrollment.ActualDelivery
    ,Forms.[2MonthQoL]
    ,[Enrollment].[ActualDelivery] + 70 AS Due
    ,IIF((DateDiff("d", [Due], DATE ())<0, NULL, (DateDiff("d", [Due], DATE ())) AS DaysOverdue
FROM Enrollment
LEFT JOIN Forms ON Enrollment.Participant_ID = Forms.Participant_IDFK
WHERE (
        ((Enrollment.ActualDelivery) IS NOT NULL)
        AND ((Forms.[2MonthQoL]) IS NULL)
        );