Re: Wrong manual info? - Mailing list pgsql-docs

"Christopher Kings-Lynne" <chriskl@familyhealth.com.au> writes:
> As far as I can tell, 'now' works perfectly as a dynamic column DEFAULT.  It
> uses insert time, NOT table creation time

Hmm.  The manual is correct as written, because it warns against writing
TIMESTAMP 'now', which indeed does not work.  In current sources I get:

regression=# create table foo (f1 int, f2 timestamp default TIMESTAMP 'now',
regression(# f3 timestamp default 'now');
CREATE
regression=# insert into foo values(1);
INSERT 139644 1
regression=# insert into foo values(2);
INSERT 139645 1
regression=# insert into foo values(3);
INSERT 139646 1
regression=# select * from foo;
 f1 |           f2           |           f3
----+------------------------+------------------------
  1 | 2001-10-08 10:36:02-04 | 2001-10-08 10:36:07-04
  2 | 2001-10-08 10:36:02-04 | 2001-10-08 10:36:08-04
  3 | 2001-10-08 10:36:02-04 | 2001-10-08 10:36:10-04
(3 rows)

regression=# \d foo
                                     Table "foo"
 Column |            Type             |                   Modifiers

--------+-----------------------------+-----------------------------------------------
 f1     | integer                     |
 f2     | timestamp(0) with time zone | default '2001-10-08 10:36:02-04'::timestamptz
 f3     | timestamp(0) with time zone | default 'now'

regression=# select * from pg_attrdef where adrelid =
regression-# (select oid from pg_class where relname = 'foo');
 adrelid | adnum |                                                          adbin
                   |                 adsrc 

---------+-------+--------------------------------------------------------------------------------------------------------------------------+---------------------------------------
  139642 |     2 | { CONST :consttype 1184 :constlen 8 :constbyval false :constisnull false :constvalue  8 [ 65 -118
-93-78 -112 0 0 0 ] } | '2001-10-08 10:36:02-04'::timestamptz 
  139642 |     3 | { CONST :consttype 705 :constlen -1 :constbyval false :constisnull false :constvalue  7 [ 0 0 0 7
110111 119 ] }        | 'now' 
(2 rows)

So TIMESTAMP 'now' does get coerced to a timestamp constant on sight,
which is what I would expect.  I find it rather surprising that the
unknown-type literal isn't getting coerced during CREATE TABLE too.
After looking at the code, I see that this is a deliberate hack to
make the world safe for DEFAULT 'now' --- see catalog/heap.c around line
1630 in current sources.  However, I think this is an ugly backwards-
compatibility hack, rather than something the manual should recommend
as preferred practice.  So I think the docs are okay as is.

            regards, tom lane