On Wed, Dec 17, 2014 at 3:11 PM, David G Johnston < david.g.johns...@gmail.com> wrote: > > Patrick Krecker wrote > > I encountered this today and it was quite surprising: > > > > select version(); > > version > > > > > ------------------------------------------------------------------------------------------------------ > > PostgreSQL 9.3.5 on x86_64-unknown-linux-gnu, compiled by gcc (Ubuntu > > 4.8.2-19ubuntu1) 4.8.2, 64-bit > > > > create table foo as (select generate_series(1,3)); > > > > As expected, the following fails: > > > > select count from foo; > > ERROR: column "count" does not exist > > LINE 1: select count from foo; > > ^ > > But if I change the syntax to something I thought was equivalent: > > > > select foo."count" from foo; > > count > > ------- > > 3 > > (1 row) > > > > It works! This was quite surprising to me. Is this expected behavior, > that > > you can call an aggregate function without any parentheses (I can't find > > any other syntax that works for count() sans parentheses, and this > > behavior > > doesn't occur for any other aggregate)? > > That fact that this is an aggregate function is beside the point - the > syntax works for any function. > > The following two expressions are equivalent: > > count(foo) = foo.count > > I do not immediately recall where this is documented but it is. It should > probably be documented or cross-referenced at: > > > http://www.postgresql.org/docs/9.3/static/sql-syntax-calling-funcs.html#SQL-SYNTAX-CALLING-FUNCS-NAMED > > but alas that is not so. > > The basic idea is to hide the function invocation and allow for > syntactically similar derived columns to be described. > > (goes looking) > > 4.2.6 - the note therein: > > http://www.postgresql.org/docs/9.3/static/sql-expressions.html#FIELD-SELECTION > pointing to 35.4.3 > > http://www.postgresql.org/docs/9.3/static/xfunc-sql.html#XFUNC-SQL-COMPOSITE-FUNCTIONS > > This relies on the rule that every table automatically has an implicit type > created and so a "composite function" can act on that type. The "foo." > reference in your example is technically referring to the type "foo" and > not > the table "foo". > > David J. > > > > > -- > View this message in context: > http://postgresql.nabble.com/Strange-error-message-when-reference-non-existent-column-foo-count-tp5831200p5831204.html > Sent from the PostgreSQL - general mailing list archive at Nabble.com. > > > -- > Sent via pgsql-general mailing list (pgsql-general@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-general
Well, that clears it up. Thanks!
