Re: ORDER BY with EXCEPT?

David E. Wheeler wrote:
> Howdy,
>
> I was just updating a function in pgTAP that, given a schema name and
> an array of function names, returns a set of those function names that
> are not in the named schema. I got it working with a subquery, and
> David Fetter suggested that I try an EXCEPT query instead. The only
> problem is that it doesn't like my ORDER BY clause. The function is:
>
> CREATE OR REPLACE FUNCTION mytest(NAME, NAME[]) RETURNS setof text AS $$
> SELECT quote_ident($2[i])
> FROM generate_series(1, array_upper($2, 1)) AS s(i)
> EXCEPT
> SELECT quote_ident(p.proname)
> FROM pg_catalog.pg_proc p
> JOIN pg_catalog.pg_namespace n
> ON p.pronamespace = n.oid
> AND quote_ident(n.nspname) = quote_ident($1)
> ORDER BY s.i
> $$ LANGUAGE SQL;
>
> When I run this, PostgreSQL 8.3 tells me:
>
> ERROR: missing FROM-clause entry for table "s"
> LINE 10: ORDER BY s.i
>
> Um, really" Have I not put the ORDER BY clause in the right place? Is
> this a bug?

The docs say
<http://www.postgresql.org/docs/current/static/sql-select.html#SQL-ORDERBY>:

"A limitation of this feature is that an ORDER BY clause applying to the
result of a UNION, INTERSECT, or EXCEPT clause can only specify an
output column name or number, not an expression."

Why not just say "order by 1" ?

cheers

andrew