Why lower's not accept an AS declaration ?

Hi,

May be my question is stupid ... but I'm a little suprised :

SELECT id_letter as letter from my_table;

letter
-----
B
C
a
A

SELECT id_letter as letter from my_table order by letter;

letter
-----
A
B
C
a

SELECT id_letter as letter from my_table order by lower(letter);

ERROR:  Attribute "letter" not found

You can imagine my test is simple, in practise it's not the reallity of my
original request ... but this example is just to show that lower() function
does not accept an AS declaration ... is it normal ?

Thanks for your answers ...

Regards,
--
Hervé Piedvache

Elma Ingénierie Informatique
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