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@sigaev.ru
  WWW: http://www.sigaev.ru/