Sum values in one field based on date range in another - ms-access

Question

I have two tables, both with dates (which is what they are/will be joined on)
Table 1 has daily rainfall values
Table 2 has weekly water volume values.
I'm trying to get Access to calculate the weekly rainfall (from the daily values) based on the dates that are given for the water volumes ie: total rainfall between two dates calculated dynamically. I have some experience with using Access SQL but I am stumped on this one. To add to the complication, every once in a while the volume values aren't always 7 days apart.

Answer 1

One method is to find the week numbers from each table, then join between these:
Select
Sum(Table1.Volume) As Volume1,
ISO_Weeknumber(Table1.[datefield]) As WeekNumber1,
Sum(Table2.Volume) As Volume2,
ISO_Weeknumber(Table2.[datefield]) As WeekNumber2
From
Table1
Inner Join
Table2
On ISO_Weeknumber(Table1.[datefield])=ISO_Weeknumber(Table2.[datefield])
Group By
ISO_Weeknumber(Table1.[datefield]),
ISO_Weeknumber(Table2.[datefield])
using this function:
Public Function ISO_WeekYearNumber( _
ByVal datDate As Date, _
Optional ByRef intYear As Integer, _
Optional ByRef bytWeek As Byte) _
As String
' Calculates and returns year and week number for date datDate according to the ISO 8601:1988 standard.
' Optionally returns numeric year and week.
' 1998-2007, Gustav Brock, Cactus Data ApS, CPH.
' May be freely used and distributed.
Const cbytFirstWeekOfAnyYear As Byte = 1
Const cbytLastWeekOfLeapYear As Byte = 53
Const cbytMonthJanuary As Byte = 1
Const cbytMonthDecember As Byte = 12
Const cstrSeparatorYearWeek As String = "W"
Dim bytMonth As Byte
Dim bytISOThursday As Byte
Dim datLastDayOfYear As Date
intYear = Year(datDate)
bytMonth = Month(datDate)
bytWeek = DatePart("ww", datDate, vbMonday, vbFirstFourDays)
If bytWeek = cbytLastWeekOfLeapYear Then
bytISOThursday = Weekday(vbThursday, vbMonday)
datLastDayOfYear = DateSerial(intYear, cbytMonthDecember, 31)
If Weekday(datLastDayOfYear, vbMonday) >= bytISOThursday Then
' OK, week count of 53 is caused by leap year.
Else
' Correct for Access97/2000+ bug.
bytWeek = cbytFirstWeekOfAnyYear
End If
End If
' Adjust year where week number belongs to next or previous year.
If bytMonth = cbytMonthJanuary Then
If bytWeek >= cbytLastWeekOfLeapYear - 1 Then
' This is an early date of January belonging to the last week of the previous year.
intYear = intYear - 1
End If
ElseIf bytMonth = cbytMonthDecember Then
If bytWeek = cbytFirstWeekOfAnyYear Then
' This is a late date of December belonging to the first week of the next year.
intYear = intYear + 1
End If
End If
ISO_WeekYearNumber = CStr(intYear) & cstrSeparatorYearWeek & Format(bytWeek, "00")
End Function
For this to work, you must have all weeks in Table1 that exist in Table2 and vice versa.