BUG #5018: Window function alias

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.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com

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