Re: function expression in FROM may not refer to other relations of same query level - Mailing list pgsql-sql

"Philippe Lang" <philippe.lang@attiksystem.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