Private Sub Search_Click()
Dim stCriteria As String
stCriteria = IIf(IsNull(Me.PeriodDateStart), "", "[tblFieldDate] >= " & CDbl(Me.PeriodDateStart) & " And ") & _
IIf(IsNull(Me.PeriodDateEnd), "", "[tblFieldDate] <= " & CDbl(Me.PeriodDateEnd) & " And ") & _
IIf(IsNull(Me.ProcessNo), "", "[tblFieldProcessNo] = " & Me.ProcessNo & " And ") & _
IIf(IsNull(Me.Person), True, "[tblFieldPerson] = '" & Me.Person & "'")
Me.subForm.Form.RecordSource = "SELECT tblField1, tblField2, ... FROM tblTable WHERE " & stCriteria
End Sub