MS Access query, how to use SQL to group single dates into weeks

Question

I currently have two tables. One has Employee Names and a number associated to that name.

The other date has time sheet date with columns for the employee number, the d

Answer 1

As the first and last week numbers cross calendar years, both year and week number must be included:

Option Compare Database
Option Explicit

    Public Const MaxWeekValue           As Integer = 53
    Public Const MinWeekValue           As Integer = 1
    Public Const MaxMonthValue          As Integer = 12
    Public Const MinMonthValue          As Integer = 1

' Returns, for a date value, a formatted string expression with
' year and weeknumber according to ISO-8601.
' Optionally, a W is used as separator between the year and week parts.
'
' Typical usage:
'
'   FormatWeekIso8601(Date)
'   ->  2017-23
'
'   FormatWeekIso8601(Date, True)
'   ->  2017W23
'
' 2017-04-28. Gustav Brock, Cactus Data ApS, CPH.
'
Public Function FormatWeekIso8601( _
    ByVal Expression As Variant, _
    Optional ByVal WeekSeparator As Boolean) _
    As String

    Const Iso8601Separator  As String = "W"
    Const NeutralSeparator  As String = "-"

    Dim Result              As String

    Dim IsoYear As Integer
    Dim IsoWeek As Integer

    If IsDate(Expression) Then
        IsoWeek = Week(DateValue(Expression), IsoYear)
        Result = _
            VBA.Format(IsoYear, String(3, "0")) & _
            IIf(WeekSeparator, Iso8601Separator, NeutralSeparator) & _
            VBA.Format(IsoWeek, String(2, "0"))
    End If

    FormatWeekIso8601 = Result

End Function

' Returns the ISO 8601 week of a date.
' The related ISO year is returned by ref.
'
' 2016-01-06. Gustav Brock, Cactus Data ApS, CPH.
'
Public Function Week( _
    ByVal Date1 As Date, _
    Optional ByRef IsoYear As Integer) _
    As Integer

    Dim Month       As Integer
    Dim Interval    As String
    Dim Result      As Integer

    Interval = "ww"

    Month = VBA.Month(Date1)
    ' Initially, set the ISO year to the calendar year.
    IsoYear = VBA.Year(Date1)

    Result = DatePart(Interval, Date1, vbMonday, vbFirstFourDays)
    If Result = MaxWeekValue Then
        If DatePart(Interval, DateAdd(Interval, 1, Date1), vbMonday, vbFirstFourDays) = MinWeekValue Then
            ' OK. The next week is the first week of the following year.
        Else
            ' This is really the first week of the next ISO year.
            ' Correct for DatePart bug.
            Result = MinWeekValue
        End If
    End If

    ' Adjust year where week number belongs to next or previous year.
    If Month = MinMonthValue Then
        If Result >= MaxWeekValue - 1 Then
            ' This is an early date of January belonging to the last week of the previous ISO year.
            IsoYear = IsoYear - 1
        End If
    ElseIf Month = MaxMonthValue Then
        If Result = MinWeekValue Then
            ' This is a late date of December belonging to the first week of the next ISO year.
            IsoYear = IsoYear + 1
        End If
    End If

    ' IsoYear is returned by reference.
    Week = Result

End Function

If you just want to pivot on the ultimo week date, you can use this expression:

DateAdd("d", 7 - Weekday([WorkDate], vbMonday), [WorkDate])

This assumes ISO week numbering where Monday is the first day of the week.