Обсуждение: date versus datetime?

Hi folks,

Would anyone have any recommendations for choosing the date type versus
the datetime type for storing date information?  I think the date type is
probably sufficient for my needs, and it seems a bit simpler and handier;
for instance, it seems I can do this with the date type:

select * from table where date_field < some_date_I_specify_here

However, if my reading of the manual and my experiments are correct, I
can't perform that sort of operation with the datetime type.  Is my
understanding correct?

Sorry for my newbie-ness...

eric

_______________________
Eric McKeown
ericm@palaver.net
http://www.palaver.net

Eric McKeown <ericm@palaver.net> writes:
> for instance, it seems I can do this with the date type:
> select * from table where date_field < some_date_I_specify_here
> However, if my reading of the manual and my experiments are correct, I
> can't perform that sort of operation with the datetime type.

You certainly can do that with datetime; I do it all the time.
Without seeing a concrete example, I'm not sure why it's not working for
you.  Perhaps you are writing the comparison date in a format that's
acceptable for type "date" but not for "datetime"?  That doesn't seem
very likely though; datetime's parser is relatively flexible.

There are a couple of gotchas in writing datetime constants in SQL
commands.  You have to put quotes around them (they're strings as
far as the parser is concerned).  For example,
    select * from ohistory where ordertime < 'jun 10 1998 16:00';
In some situations you may have to explicitly cast the string constant
to datetime type:
    select * from ohistory where ordertime < 'jun 10 1998 16:00'::datetime;
but I find Postgres usually manages to figure out for itself that a
datetime value is wanted.

As far as I know those gotchas also apply to date constants, however.
So I'm still confused about why one works and not the other for you.

            regards, tom lane