Re: function expression in FROM may not refer to other relations of same query level

Thanks a lot for your support. With a subselect and offset 0, the function is called only once per row, that's fine.

Here is the final test code, in case it can help anyone.

-----------------------------------------------

CREATE TYPE public.lines AS
(
line1 varchar(10),
line2 varchar(10)
);

CREATE TABLE public.tbl
(
id int4 PRIMARY KEY,
usr varchar(10),
code int4
) WITHOUT OIDS;

CREATE FUNCTION public.get_lines(int4)
RETURNS lines AS
'
DECLARE

code ALIAS FOR $1;

lines lines%rowtype;

BEGIN

IF code = 1 THEN
lines.line1 = ''A'';
lines.line2 = ''B'';
ELSE
lines.line1 = ''Z'';
lines.line2 = ''Z'';
END IF;

RAISE NOTICE ''-------> get_lines was called...'';

RETURN lines;

END;
'
LANGUAGE 'plpgsql' VOLATILE;

INSERT INTO tbl VALUES (1, 'one', 1);
INSERT INTO tbl VALUES (2, 'two', 2);
INSERT INTO tbl VALUES (3, 'three', 1);
INSERT INTO tbl VALUES (4, 'four', 2);

select
id,
usr,
code,
(get_lines_data).line1,
(get_lines_data).line2

from
(
select
id,
usr,
code,
get_lines(code) as get_lines_data

from tbl
offset 0
)
as ss;

-----------------------------------------------

Philippe Lang

-----Message d'origine-----
De : Tom Lane [mailto:tgl(at)sss(dot)pgh(dot)pa(dot)us]
Envoyé : jeudi, 12. août 2004 16:31
À : Philippe Lang
Cc : pgsql-sql(at)postgresql(dot)org
Objet : Re: [SQL] function expression in FROM may not refer to other relations of same query level

"Philippe Lang" <philippe(dot)lang(at)attiksystem(dot)ch> writes:
> I wish there was a way to run the query like this:

> select
> id,
> usr,
> code,
> CAST(get_lines(code) as lines)
> from tbl;

You can do something like this:

regression=# create type complex as (r float8, i float8); CREATE TYPE regression=# create function fooey(float8) returns complex as regression-# 'select $1 + 1, $1 + 2' language sql; CREATE FUNCTION regression=# select f1, (fooey).r, (fooey).i from regression-# (select f1, fooey(f1) as fooey from float8_tbl) ss;
f1 | r | i
-----------------------+-----------------------+-----------------------
0 | 1 | 2
-34.84 | -33.84 | -32.84
-1004.3 | -1003.3 | -1002.3
-1.2345678901234e+200 | -1.2345678901234e+200 | -1.2345678901234e+200
-1.2345678901234e-200 | 1 | 2
(5 rows)

Note the odd-looking parenthesization --- you can't write just "fooey.r"
because that looks like it should be a table and field name, not a field name that is selected from.

If the sub-select is too simple, as it is in this case, the planner is likely to "flatten out" the query into

select f1, (fooey(f1)).r, (fooey(f1)).i from float8_tbl;

thus defeating your purpose of not calling the function twice. The currently best hack for preventing this is to add "OFFSET 0" to the
sub-select:

select f1, (fooey).r, (fooey).i from
(select f1, fooey(f1) as fooey from float8_tbl offset 0) ss;

regards, tom lane