Thread: copy command & null datetime

The following example will cause COPY to fail on input:

xxx|yyy|zzz||aaa|bbb|

where the empty field in between zzz & aaa is of type datetime (don't know
about other types). I know a \N will fix this, but interpreting an empty
import field as NULL would certainly beef up COPY as other database systems
don't output the \N which is unique to PostgreSQL. Wish list item?

Ken

On Sun, 7 Mar 1999, Ken J. Wright wrote:

> The following example will cause COPY to fail on input:
>
> xxx|yyy|zzz||aaa|bbb|
>
> where the empty field in between zzz & aaa is of type datetime (don't know
> about other types). I know a \N will fix this, but interpreting an empty
> import field as NULL would certainly beef up COPY as other database systems
> don't output the \N which is unique to PostgreSQL. Wish list item?

Yes, I discovered this little issue the other day.  What is this \N
option, though?  I have some 900000+ records out of a 2.1 million row
table that have NULL date fields.  I ended up sticking in a dummy date (of
like 1901) for those, because I knew that valid dates stopped at a
particular lower cutoff date of around 1968, then ignore the earlier date
altogether.

Brett W. McCoy
                                        http://www.lan2wan.com/~bmccoy/
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"Ken J. Wright" <ken@ori-ind.com> writes:
> where the empty field in between zzz & aaa is of type datetime (don't know
> about other types). I know a \N will fix this, but interpreting an empty
> import field as NULL would certainly beef up COPY as other database systems
> don't output the \N which is unique to PostgreSQL.

You might call that "beefing up COPY" but I'd call it "breaking COPY".
For data types such as text or varchar, there is a considerable
difference between an empty field value and a NULL field.  You
propose to make it impossible to tell the difference.

IMHO, COPY's primary responsibility is to serve as a lossless conduit
for saving and restoring databases, not to be a user-friendly or
foreign-database-compatible data import method.  It *must* reliably
distinguish empty strings from NULL fields.  If there's some other
data format you want to read, you can use a preprocessor to convert
it into COPY format or INSERT statements.

Now I'm certainly not particularly in love with the \N notation,
and if you have a better idea I'm all ears.  But failing to
distinguish empty and NULL is not a better idea.

            regards, tom lane