>I don't know exactly WHY, I just know that you should not use it.
>
>Here was a question, BTW, may be you can explain
>
>message #1387014
>
>It's not an issue of the phrase "GROUP_ID" per se...you CAN'T use an expression alias in a GROUP BY. Period. You could even try to call it "Fred", and say...
>
>SELECT MyField as Fred, sum(amount) as totamount
> from mytable
> group by Fred
>
>...and it will bomb like Bristol Palin's boyfriend's condom. You have to refer to the original column name (or expression)

I know it will bomb (tried it too), but any scientific explanation behind this behavior?