On Sat, Jun 25, 2016 at 12:44 AM, Robert Haas <robertmh...@gmail.com> wrote:

> On Wed, Jun 22, 2016 at 4:11 AM, Amit Langote
> <langote_amit...@lab.ntt.co.jp> wrote:
> >> In an outer join we have to differentiate between a row being null
> (because
> >> there was no joining row on nullable side) and a non-null row with all
> >> column values being null. If we cast the whole-row expression to a text
> >> e.g. r.*::text and test the resultant value for nullness, it gives us
> what
> >> we want. A null row casted to text is null and a row with all null
> values
> >> casted to text is not null.
> >
> > You are right.  There may be non-null rows with all columns null which
> are
> > handled wrongly (as Rushabh reports) and the hack I proposed is not right
> > for.  Especially if from non-nullable side as in the reported case, NULL
> > test for such a whole-row-var would produce the wrong result.  Casting to
> > text as your patch does produces the correct behavior.
> I agree, but I think we'd better cast to pg_catalog.text instead, just
> to be safe.  Committed that way.

postgres_fdw resets the search path to pg_catalog while opening connection
to the server. The reason behind this is explained in deparse.c

 * We assume that the remote session's search_path is exactly "pg_catalog",
 * and thus we need schema-qualify all and only names outside pg_catalog.

So, we should not be schema-qualifying types while casting. From deparse.c
 * Convert type OID + typmod info into a type name we can ship to the remote
 * server.  Someplace else had better have verified that this type name is
 * expected to be known on the remote end.
 * This is almost just format_type_with_typemod(), except that if left to
 * own devices, that function will make schema-qualification decisions based
 * on the local search_path, which is wrong.  We must schema-qualify all
 * type names that are not in pg_catalog.  We assume here that built-in
 * are all in pg_catalog and need not be qualified; otherwise, qualify.
static char *
deparse_type_name(Oid type_oid, int32 typemod)
    if (is_builtin(type_oid))
        return format_type_with_typemod(type_oid, typemod);
        return format_type_with_typemod_qualified(type_oid, typemod);

Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company

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