I'm using postgres 7.0.2 on a FreeBSD 4.0-STABLE system. Compiled
with gcc version 2.95.2 19991024 (release).
When I create a table with a default timestamp of 'now' it works as
expected. When I create it with the timestamp 'now'::timestamp
explicitly specifying the type, it evaluates this to the actual time
I create the table:
> create table test (a int4,test timestamp default 'now');
CREATE
> create table test1 (a int4,test timestamp default 'now'::timestamp);
CREATE
> \d test
Table "test"
Attribute | Type | Modifier
-----------+-----------+---------------
a | integer |
test | timestamp | default 'now'
fastmail=> \d test1
Table "test1"
Attribute| Type | Modifier
---------+-----------+-----------------------------------------------
a | integer |
test | timestamp | default '2000-08-18 13:24:16-04'::"timestamp"
My guess is that it's performing the conversion and interpretation of
the default expression when the table is created. This is a good
thing if you have a constant expression, ie default 1+2. However, an
expression that is not constant should not be evaluated until the
insertion is performed.
Something like default 'now'::timestamp-'1 year'::timespan is odd
because it evaluates the 'now' but not the entire function:
default ('2000-08-18 13:28:41-04'::"timestamp" - '1 year
00:00'::"interval")
A simple addition:
create table test3 (a int4 default 1+2,test timestamp);
Yields an already evaluated expression:
a | integer | default 3
-Michael
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