Re: Sort problem

Jean-Luc Lachance <jllachan(at)nsd(dot)ca> writes:
> Can someone (Tom maybe) please tell me why one can not use an alias from
> the select list in the where clause or the order by clause.

Eh? You can do it in the ORDER BY clause:

regression=# select f1 as alias from int4_tbl order by alias;
alias
-------------
-2147483647
-2147483647
-123456
-123456
0
0
123456
123456
2147483647
2147483647
(10 rows)

As for WHERE, the reason you can't do it there is that it wouldn't be
meaningful. The SELECT list is not calculated until *after* the WHERE
conditions are applied. Any SQL book should tell you about the stages
of processing of a SELECT query...

regards, tom lane