Using a case statement in the group by - sql

Question

I have the below sql. I am wanting my results to be grouped if the boolean is checked 0, but not grouped if the boolean is checked 1. Is the code below a good way of doing this? I feel like it should work but it is throwing the error "InvoicePeriodID is invalid in the select list because it is not contained in an aggraagte function or group by" Any advice?
----insert invoices for rebates grouped by date, address, contract, rebate note, and order type
declare #invoices table(InvoicePeriodID int, InvoiceStartDate datetime, InvoiceEndDate datetime, JDEAddressNo float, ContractID int, RebateNoteID int, JDEOrderType char(2), RebateInvoiceID int)
insert #invoices (InvoicePeriodID , InvoiceStartDate , InvoiceEndDate , JDEAddressNo , ContractID , RebateNoteID, JDEOrderType)
select
i.InvoicePeriodID
, i.InvoiceStartDate
, i.InvoiceEndDate
, i.JDEAddressNo
, i.ContractID
, i.RebateNoteID
, i.JDEOrderType
from
#inv i
group by
case i.InvoiceSeparately
when 1 then null
when 0 then i.InvoicePeriodID
end
, case i.InvoiceSeparately
when 1 then null
when 0 then i.InvoiceStartDate
end
, case i.InvoiceSeparately
when 1 then null
when 0 then i.InvoiceEndDate
end
, case i.InvoiceSeparately
when 1 then null
when 0 then i.JDEAddressNo
end
, case i.InvoiceSeparately
when 1 then null
when 0 then i.ContractID
end
, case i.InvoiceSeparately
when 1 then null
when 0 then i.RebateNoteId
end
, case i.InvoiceSeparately
when 1 then null
when 0 then i.JDEOrderType
end

Answer 1

I think it is more readable and easier to do what you want this way
select
i.InvoicePeriodID
, i.InvoiceStartDate
, i.InvoiceEndDate
, i.JDEAddressNo
, i.ContractID
, i.RebateNoteID
, i.JDEOrderType
from
#inv i
WHERE i.InvoiceSeparately = 0
group BY i.InvoicePeriodID
,i.InvoiceStartDate
,i.InvoiceEndDate
, i.JDEAddressNo
, i.ContractID
,i.RebateNoteId
, i.JDEOrderType
UNION ALL
select
i.InvoicePeriodID
, i.InvoiceStartDate
, i.InvoiceEndDate
, i.JDEAddressNo
, i.ContractID
, i.RebateNoteID
, i.JDEOrderType
from
#inv i
WHERE i.InvoiceSeparately = 1