Обсуждение: Problem with aliasing

I wrote a plpgsql function to return the maximum of three dates.

TAL=# select max(req_del_date1, req_del_date2, req_del_date3) as ma1
from invoices;
     ma1
------------
  2003-02-25
  2003-02-25
(2 rows)


However I'm having problems with the following query:

TAL=# select max(req_del_date1, req_del_date2, req_del_date3) as max
from invoices where max <= now();
ERROR:  Attribute "max" not found

Why can't the where part of the query see "max"? I've tried aliasing the
returned value but that did not work either:

TAL=# select max(req_del_date1, req_del_date2, req_del_date3) as ma1
from invoices where ma1 <= now();
ERROR:  Attribute "ma1" not found

What is wrong with my syntax?

Thanks!

Jc

Jean-Christian Imbeault <jc@mega-bucks.co.jp> writes:

> TAL=# select max(req_del_date1, req_del_date2, req_del_date3) as ma1 from
> invoices where ma1 <= now();
> ERROR:  Attribute "ma1" not found
>
> What is wrong with my syntax?

Try either of:

  SELECT max(req1, req2, req3) AS max FROM invoices WHERE max(req1, req2, req3) <= now()
  SELECT * from (select max(req1, req2, req3) AS max FROM invoices) WHERE max <= now()

Whichever seems clearer to you, I think postgres actually runs the two the
same way. Note, you should mark your function immutable so postgres knows it
can optimize the second case into the first.

--
greg

Greg Stark wrote:
>
> Try either of:
>
>   SELECT max(req1, req2, req3) AS max FROM invoices WHERE max(req1, req2, req3) <= now()

Ok, that works. But why can't I alias the result of the max() function
and use the alias in the where clause? Something like:

SELECT max(r1,r2,r3) as max from invoices WHERE max <= now();

Why can't postgres see the alias when inside the WHERE clause?

Jc

On 21 Feb 2003, Greg Stark wrote:

> Jean-Christian Imbeault <jc@mega-bucks.co.jp> writes:
>
> > TAL=# select max(req_del_date1, req_del_date2, req_del_date3) as ma1 from
> > invoices where ma1 <= now();
> > ERROR:  Attribute "ma1" not found
> >
> > What is wrong with my syntax?
>
> Try either of:
>
>   SELECT max(req1, req2, req3) AS max FROM invoices WHERE max(req1, req2, req3) <= now()
>   SELECT * from (select max(req1, req2, req3) AS max FROM invoices) WHERE max <= now()
>
> Whichever seems clearer to you, I think postgres actually runs the two the
> same way. Note, you should mark your function immutable so postgres knows it
> can optimize the second case into the first.

Doesn't:

SELECT max(req1, req2, req3) AS ma1 FROM invoices HAVING ma1 <= now();

work?

Now I'm going to have to go see if I've got that wrong as well...


--
Nigel J. Andrews

On Fri, 21 Feb 2003, Nigel J. Andrews wrote:

> On 21 Feb 2003, Greg Stark wrote:
>
> > Jean-Christian Imbeault <jc@mega-bucks.co.jp> writes:
> >
> > > TAL=# select max(req_del_date1, req_del_date2, req_del_date3) as ma1 from
> > > invoices where ma1 <= now();
> > > ERROR:  Attribute "ma1" not found
> > >
> > > What is wrong with my syntax?
> >
> > Try either of:
> >
> >   SELECT max(req1, req2, req3) AS max FROM invoices WHERE max(req1, req2, req3) <= now()
> >   SELECT * from (select max(req1, req2, req3) AS max FROM invoices) WHERE max <= now()
> >
> > Whichever seems clearer to you, I think postgres actually runs the two the
> > same way. Note, you should mark your function immutable so postgres knows it
> > can optimize the second case into the first.
>
> Doesn't:
>
> SELECT max(req1, req2, req3) AS ma1 FROM invoices HAVING ma1 <= now();
>
> work?
>
> Now I'm going to have to go see if I've got that wrong as well...

Obviously I got the wrong end of the stick but any way, I was wrong that column
aliases could be used for group by and having clauses. At least that's what
7.2.3 is telling me.


--
Nigel J. Andrews