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Document a limitation of COPY's new CSV mode. Doc patch from Andrew

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Dunstan, editorializing by Neil Conway.
This commit is contained in:
Neil Conway 2004-11-17 02:50:06 +00:00
parent b25d23e1e6
commit a51e54cf5b
1 changed files with 19 additions and 13 deletions
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32
doc/src/sgml/ref/copy.sgml
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@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/copy.sgml,v 1.58 2004/11/15 06:32:15 neilc Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/copy.sgml,v 1.59 2004/11/17 02:50:06 neilc Exp $
PostgreSQL documentation
-->
@ -433,13 +433,13 @@ COPY <replaceable class="parameter">tablename</replaceable> [ ( <replaceable cla
</para>
<para>
It is strongly recommended that applications generating COPY data convert
It is strongly recommended that applications generating <command>COPY</command> data convert
data newlines and carriage returns to the <literal>\n</> and
<literal>\r</> sequences respectively. At present it is
possible to represent a data carriage return by a backslash and carriage
return, and to represent a data newline by a backslash and newline.
However, these representations might not be accepted in future releases.
They are also highly vulnerable to corruption if the COPY file is
They are also highly vulnerable to corruption if the <command>COPY</command> file is
transferred across different machines (for example, from Unix to Windows
or vice versa).
</para>
@ -484,15 +484,16 @@ COPY <replaceable class="parameter">tablename</replaceable> [ ( <replaceable cla
<para>
In general, the <literal>CSV</> format has no way to distinguish a
<literal>NULL</> from an empty string.
<productname>PostgreSQL</productname>'s COPY handles this by
quoting. A <literal>NULL</> is output as the <literal>NULL</> string
and is not quoted, while a data value matching the <literal>NULL</> string
is quoted. Therefore, using the default settings, a <literal>NULL</> is
written as an unquoted empty string, while an empty string is
written with double quotes (<literal>""</>). Reading values follows
similar rules. You can use <literal>FORCE NOT NULL</> to prevent <literal>NULL</>
input comparisons for specific columns.
<literal>NULL</> value from an empty string.
<productname>PostgreSQL</>'s <command>COPY</> handles this by
quoting. A <literal>NULL</> is output as the <literal>NULL</>
string and is not quoted, while a data value matching the
<literal>NULL</> string is quoted. Therefore, using the default
settings, a <literal>NULL</> is written as an unquoted empty
string, while an empty string is written with double quotes
(<literal>""</>). Reading values follows similar rules. You can
use <literal>FORCE NOT NULL</> to prevent <literal>NULL</> input
comparisons for specific columns.
</para>
<note>
@ -500,7 +501,12 @@ COPY <replaceable class="parameter">tablename</replaceable> [ ( <replaceable cla
CSV mode will both recognize and produce CSV files with quoted
values containing embedded carriage returns and line feeds. Thus
the files are not strictly one line per table row like text-mode
files.
files. However, <productname>PostgreSQL</productname> will reject
<command>COPY</command> input if any fields contain embedded line
end character sequences that do not match the line ending
convention used in the CSV file itself. It is generally safer to
import data containing embedded line end characters using the
text or binary formats rather than CSV.
</para>
</note>