Re: why can a named subselect not be used in a where

Markus,

> cenes_test=> select personen.*, (select max(last_visit) from sessions
> where sessions.personen_id = personen.personen_id) as max from
>  personen
> where max between 1009148400 and 1011913200 order by max desc;
> ERROR:  Attribute 'max' not found
> 
> I again think that the table structure is not neccesary to understand
>  my
> question.
> 
> Well, why can't I use max in the where clause?

There's two problems with the above query that have nothing to do withnamed subselects, which are well-supported by
PostgreSQL(in fact, asof 7.1.3, Postgres has better support for subselects of all sorts thanany other major RDBMS
platform).

1. "Max" is a reserved word in SQL.  You are confusing the parser. Pick another name.

2. While you are already aware that the example query is not the mostefficient construction, I also think you are doing
youraliasing inthe wrong place:
 
select personen.*, (select max(last_visit) as max_visit from sessionswhere sessions.personen_id = personen.personen_id)
frompersonen
 
... but I could be wrong, as I almost never find any reason to use asub-select in the SELECT line.

-Josh

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