On 4/3/07, Bruce Momjian <bruce@momjian.us> wrote:
>
> Because this patch was not completed, I have added it to the TODO list:
>
> * Fix to_date()-related functions to consistently issue errors
>
> http://archives.postgresql.org/pgsql-hackers/2007-02/msg00915.php
I'm now taking another run at this issue. Here's what I've got in mind.
There are three distinct conventions for specifying a date that we
consider in Postgres. These are* Julian day,* ISO week date, and* Standard Gregorian.
Within an ISO week date, you can identify a date using either* year, week and day-of-week, or* year and day-of-year.
Likewise within a Gregorian date, you can identify a date using* year, month and day-of-month,* year, month,
week-of-monthand day-of-week (extremely weird, but there it is)* year, week, and day-of-week, or* year and
day-of-year.
Chad Wagner mentioned that Oracle will allow a combination of Julian
and Gregorian formats so long as both formats yield the same date. If
we're going to stick with the theme of imitating Oracle, I propose the
following:
* No mixing of Gregorian and ISO fields permitted. If the format
string contains both Gregorian and ISO normative fields in any
sequence or combination, we throw an ERRCODE_INVALID_DATETIME_FORMAT
and reject the query.* Either Gregorian or ISO format strings may include a Julian date
field, as long as the results are in agreement. If the results
disagree, we reject the query.* Purely non-normative fields (like "Q") are completely and silently
disregarded.* A Gregorian or ISO format may be over-constraining as long as all
values are in agreement. If there are any conflicts we reject the
query.
So, for example, we would reject something like "YYYY-IDDD" out of
hand because it combines the ISO and Gregorian conventions, making it
impossible to ascertain what the user really wants to do.
We would allow YYYY-MM-DD J as long as the result for the YYYY-MM-DD
part matches the result for the J part.
We would also allow something like YYYY-MM-DD D as long as the results
of YYYY-MM-DD and D matched. So to_date('2007-07-18 4', 'YYYY-MM-DD
D') would successfully return the date 18 July 2007, but if you tried
to_date('2007-07-18 5', 'YYYY-MM-DD D') you would get an error.
If there are no objections I'd be happy to cook a patch up.
