Interesting optimizer's supposition in 8.1

Tsearch2 has function to_tsquery defined as:
CREATE FUNCTION to_tsquery(oid, text)
RETURNS tsquery
AS '$libdir/tsearch2'
LANGUAGE 'c' with (isstrict,iscachable);

And let we take 2 essential equivalent queries:

# explain select book.id from to_tsquery('foo') as t, book where book.fts @@ t;
QUERY PLAN
--------------------------------------------------------------------
Nested Loop (cost=13.19..6550.69 rows=290 width=4)
Join Filter: ("inner".fts @@ "outer".t)
-> Function Scan on t (cost=0.00..12.50 rows=1000 width=32)
-> Materialize (cost=13.19..16.09 rows=290 width=36)
-> Seq Scan on book (cost=0.00..12.90 rows=290 width=36)
# explain select book.id from book where book.fts @@ to_tsquery('foo');
QUERY PLAN
-----------------------------------------------------
Seq Scan on book (cost=0.00..13.62 rows=1 width=4)
Filter: (fts @@ '''foo'''::tsquery)

Why planner suppose that t 'table' will return 1000 rows? Obviosly that function
returns only one value because of itsn't marked as 'returns setof'.

--
Teodor Sigaev E-mail: teodor(at)sigaev(dot)ru
WWW: http://www.sigaev.ru/