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List:       postgresql-sql
Subject:    Re: [SQL] Re: How do I COPY empty Datetimes?
From:       Postgres DBA <postgres () nest ! bistbn ! com>
Date:       1998-11-22 12:35:12
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On Sat, 21 Nov 1998, Tom Lane wrote:

> f.ermini@telemaco.it writes:
> > Hi all. I have a problem here. I have to automatize the periodical COPY
> > of a large set of ASCII data in a postgres database. The parser digests
> > everything I put in there, with an exception: if there is a DateTime
> > field that is empty, the copy of the field fails for a "Invalid datetime
> > format". The field isn't a NOT NULL one, so I have to accept also empty
> > values... I've tried with the sequence '', "", or simply /t/t (tab is
> > the field separator in those ASCII data), but the output has always been
> > the same. 
> 
> There's no such thing as an "empty" value of datetime.  What you can
> put in is a NULL, which is not a datetime at all, but an indicator that
> the field has no data in this particular table row.  NULLs work for any
> data type.  The syntax for a NULL field in COPY is "\N".  (Simply
> leaving the field blank, as you were trying to do, isn't good enough
> since there would be no way to distinguish an empty text field from a
> NULL text field.)
> 
> For example, here are a couple of rows of COPY data from a database of
> my own.  There are four datetime columns in the table, and these rows
> have different subsets of the four non-null (as well as nulls in several
> other columns):
> 
> 37	16	16	Fri Nov 13 17:00:07 1998 EST	EDF	29	S	7343	\N	s	7100	100	f	I	188	Mon Nov \
> 16 07:46:38 1998 EST	\N	\N	\N	\N 63	8	8	Thu Nov 12 16:00:10 1998 \
> EST	EDF	49	s	11353	\N	S	12408	100	f	C	189	\N	\N	Mon Nov 16 07:46:45 1998 EST	\N	\N 
> Apologies if your mailer mangles the data --- there are supposed to be
> two long lines with tabs in them.
> 
I think, you  could also consider using 'infinity' or '-infinity'
values for empty DATETIME fields ( choice is depending on what kind
of dates you plan to store )

Aleskey


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