Re: BUG #5018: Window function alias

Heikki Linnakangas <heikki.linnakangas@enterprisedb.com> writes:
> Marko Tiikkaja wrote:
>> I came across this:
>>
>> => SELECT lead(foo) OVER(ORDER BY foo) AS foo FROM (VALUES(0)) bar(foo);
>> ERROR:  window functions not allowed in window definition
>>
>> Changing the *column alias* to something else gives the expected answer. Is
>> this really the desired behaviour?

> It makes sense if you refer another column:

> SELECT foo*2 AS col1, lead(foo) OVER(ORDER BY col1) AS foo
> FROM (VALUES(0), (1)) bar(foo);

> I'm not sure what the SQL spec says about that, but it seems OK to me.

I think it's a bug.  If you change it to this, it doesn't complain:

regression=# SELECT lead(foo) OVER(ORDER BY foo) AS fool FROM (VALUES(0)) bar(foo);
 fool
------

(1 row)

We're getting bit by interpreting window-function ORDER BY arguments
according to SQL92 rules, in which they could refer to output-column
aliases.  This clearly has the potential to introduce circularity,
as here.  I think it would probably be best if we use strict SQL99
interpretation: window function PARTITION/ORDER arguments cannot be
interpreted as output-column names or numbers.

            regards, tom lane