On Thu, Sep 3, 2009 at 13:19, Andrew Dunstan<and...@dunslane.net> wrote: > > > Magnus Hagander wrote: >> >> Our documentation for COPY >> (http://www.postgresql.org/docs/8.4/static/sql-copy.html) has the >> following to say: >> " >> The CSV format has no standard way to distinguish a NULL value from >> an empty string. PostgreSQL's COPY handles this by quoting. A NULL is >> output as the NULL string and is not quoted, while a data value >> matching the NULL string is quoted. Therefore, using the default >> settings, a NULL is written as an unquoted empty string, while an >> empty string is written with double quotes (""). Reading values >> follows similar rules. You can use FORCE NOT NULL to prevent NULL >> input comparisons for specific columns. >> " >> >> Shouldn't that be: >> "A NULL is output as the NULL string and is not quoted, while a data >> value matching the empty string is quoted"? >> >> If not, then what really is the difference between a NULL and a NULL >> string? >> >> > > > No, it shouldn't. Let's say NULL is represented as "foo". Then a null > between delimiters will be written as > > delimiter foo delimiter > > while the string "foo" will be > > delimiter quotechar foo quotechar delimiter > > and an empty non-null string will be > > delimiter delimiter > > unless you have FORCE QUOTE on for it, in which case it will be > > delimiter quotechar quotechar delimiter > > > We had quite a bit of debate on the shape of CSV output at the time it was > done (during 8.0), and that's what we came up with. It has the useful > property that we can round-trip the data, i.e. we can read back the data we > output without losing information about nulls, no matter what the NULL > string is, something we have always been resistant to changing. > > If you think we could explain it better, by all means have a go at it. But > your proposed change isn't accurate. Here is an illustration of the above:
Oh, hang on, "the NULL string" refers to the copy parameter? Not a part of the data? I read it as "a string being NULL". Maybe something like "the value of the NULL string parameter" to be overly clear for people like me? :-) (FWIW, I totally agree with the feature, I was just confused by the docs) -- Magnus Hagander Me: http://www.hagander.net/ Work: http://www.redpill-linpro.com/ -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
