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Add "(assuming <varname>standard_conforming_strings</> is

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<literal>off</>)" clauses for bytea.
This commit is contained in:
Bruce Momjian 2006-11-23 04:27:33 +00:00
parent 5f78aa5acf
commit ab79444e7b
1 changed files with 31 additions and 28 deletions
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59
doc/src/sgml/datatype.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/datatype.sgml,v 1.180 2006/10/23 18:10:30 petere Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/datatype.sgml,v 1.181 2006/11/23 04:27:33 momjian Exp $ -->
<chapter id="datatype">
<title id="datatype-title">Data Types</title>
@ -1097,15 +1097,17 @@ SELECT b, char_length(b) FROM test2;
</para>
<para>
When entering <type>bytea</type> values, octets of certain values
<emphasis>must</emphasis> be escaped (but all octet values
<emphasis>can</emphasis> be escaped) when used as part of a string
literal in an <acronym>SQL</acronym> statement. In general, to
escape an octet, it is converted into the three-digit octal number
equivalent of its decimal octet value, and preceded by two
backslashes. <xref linkend="datatype-binary-sqlesc"> shows the
characters that must be escaped, and gives the alternate escape
sequences where applicable.
When entering <type>bytea</type> values, octets of certain
values <emphasis>must</emphasis> be escaped (but all octet
values <emphasis>can</emphasis> be escaped) when used as part
of a string literal in an <acronym>SQL</acronym> statement. In
general, to escape an octet, it is converted into the three-digit
octal number equivalent of its decimal octet value, and preceded
by two backslashes (or one backslash if
<varname>standard_conforming_strings</> is <literal>off</>).
<xref linkend="datatype-binary-sqlesc"> shows the characters
that must be escaped, and gives the alternate escape sequences
where applicable.
</para>
<table id="datatype-binary-sqlesc">
@ -1168,24 +1170,25 @@ SELECT b, char_length(b) FROM test2;
</para>
<para>
The reason that you have to write so many backslashes, as shown in
<xref linkend="datatype-binary-sqlesc">, is that an input string
written as a string literal must pass through two parse phases in
the <productname>PostgreSQL</productname> server. The first
backslash of each pair is interpreted as an escape character by
the string-literal parser and is therefore consumed, leaving the
second backslash of the pair. The remaining backslash is then
recognized by the <type>bytea</type> input function as starting
either a three digit octal value or escaping another backslash.
For example, a string literal passed to the server as
<literal>'\\001'</literal> becomes <literal>\001</literal> after
passing through the string-literal parser. The
<literal>\001</literal> is then sent to the <type>bytea</type>
input function, where it is converted to a single octet with a
decimal value of 1. Note that the apostrophe character is not
treated specially by <type>bytea</type>, so it follows the normal
rules for string literals. (See also <xref
linkend="sql-syntax-strings">.)
The reason that you have to write so many backslashes, as shown
in <xref linkend="datatype-binary-sqlesc">, is that an input
string written as a string literal must pass through two parse
phases in the <productname>PostgreSQL</productname> server.
The first backslash of each pair is interpreted as an escape
character by the string-literal parser (assuming
<varname>standard_conforming_strings</> is <literal>off</>)
and is therefore consumed, leaving the second backslash of the
pair. The remaining backslash is then recognized by the
<type>bytea</type> input function as starting either a three
digit octal value or escaping another backslash. For example,
a string literal passed to the server as <literal>'\\001'</literal>
becomes <literal>\001</literal> after passing through the
string-literal parser. The <literal>\001</literal> is then sent
to the <type>bytea</type> input function, where it is converted
to a single octet with a decimal value of 1. Note that the
apostrophe character is not treated specially by <type>bytea</type>,
so it follows the normal rules for string literals. (See also
<xref linkend="sql-syntax-strings">.)
</para>
<para>