Query Syntax & Use Of Variables

All,

I've become aware that if I create a variable in the select statement like this in Access:

SELECT Table1.ID, Sum([A]+[B]+[C]) AS TotSum

That I cannot reliably use said variable later in the same statement:

SELECT Table1.ID, Sum([A]+[B]+[C]) AS TotSum
FROM Table1
GROUP BY Table1.ID
ORDER BY TotSum DESC;

It will ask me to "enter a parameter value" for TotSum. When I do, in this example, it still sorts in correctly, but in a larger more detailed query it gets a little confused. I instead have to re-use the equation like this:

SELECT Table1.ID, Sum([A]+[B]+[C]) AS TotSum
FROM Table1
GROUP BY Table1.ID
ORDER BY Sum([A]+[B]+[C]) DESC;

Is there a way around this? It seems inefficient to recompute the sum 2 times where I think I only need to do it once.

Any input or explanations?

-BT.