Выбрать соответствующий курс валюты

SELECT top 1 FROM ТаблицаКурсов
WHERE [ПолеДаты] < DATE() AND [КодВалюты]=1
ORDER BY [ПолеДаты] DESC

SELECT Заказы.*, 
       (SELECT КурсВалюты 
        FROM CurRates 
        WHERE КодВалюты=1 AND ДатаКурса=DMax("ДатаКурса","CurRates","ДатаКурса<=" & ДатаЗаказа))

SELECT Ord.OrdID, Ord.OrderDate AS OD,
           (SELECT FIRST(Q1.CurRate)
            FROM (SELECT CurRates.CurRate, CurRates.DateFld
                        FROM CurRates
                        WHERE CurRates.DateFld<Ord.OD AND CurRates.CurId =1
                        ORDER BY CurRates.DateFld DESC) AS Q1) AS Rate
FROM Orders AS Ord;

SELECT Ord.OrdID, Ord.ImportDate,
           
            (SELECT CurRates.CurRate
                        FROM CurRates
                        WHERE CurRates.CurId =1 AND CurRates.DateFld = DMax ( " DateFld ", " CurRates ", 
                                       " DateFld <= " & Ord.ImportDate ) ) AS Rate
FROM Orders AS Ord;

SELECT Ord.OrdID,Ord.ImportDate,        
       (SELECT CurRate
        FROM CurRates
        WHERE CurId=1 AND 
              DateFld=DMax("DateFld","CurRates","DateFld<=" & Format(Ord.ImportDate,"\#mm\/dd\/yyyy\#"))) 
       AS Rate
FROM Orders AS Ord;