aggregate / count rows grouped by geography (or geometry) - sql-server

Question

I have a table such as:
Create Table SalesTable
( StuffID int identity not null,
County geography not null,
SaleAmount decimal(12,8) not null,
SaleTime datetime not null )
It has a recording of every sale with amount, time, and a geography of the county that the sale happened in.
I want to run a query like this:
Select sum(SaleAmount), County from SalesTable group by County
But if I try to do that, I get:
The type "geography" is not comparable. It cannot be used in the GROUP BY clause.
But I'd like to know how many sales happened per county. Annoyingly, if I had the counties abbreviated (SDC,LAC,SIC, etc) then I could group them because it would simply be a varchar. But then I use the geography datatype for other reasons.

Answer 1

There's a function to work with geography type as char
try this
Select sum(SaleAmount), County.STAsText() from SalesTable
group by County.STAsText()

Answer 2

I would propose a slightly different structure:
create table dbo.County (
CountyID int identity not null
constraint [PK_County] primary key clustered (CountyID),
Name varchar(200) not null,
Abbreviation varchar(10) not null,
geo geography not null
);
Create Table SalesTable
(
StuffID int identity not null,
CountyID int not null
constraint FK_Sales_County foreign key (CountyID)
references dbo.County (CountyID),
SaleAmount decimal(12,8) not null,
SaleTime datetime not null
);
From there, your aggregate looks something like:
Select c.Abbreviation, sum(SaleAmount)
from SalesTable as s
join dbo.County as c
on s.CountyID = c.CountyID
group by c.Abbreviation;
If you really need the geography column in the aggregate, you're a sub-query or a common table expression away:
with s as (
Select c.CountyID, c.Abbreviation,
sum(s.SaleAmount) as [TotalSalesAmount]
from SalesTable as s
join dbo.County as c
on s.CountyID = c.CountyID
group by c.Abbreviation
)
select s.Abbreviation, s.geo, s.TotalSalesAmount
from s
join dbo.County as c
on s.CountyID = s.CountyID;