Sophie: postgresql8.4-docs-8.4.12-0.1mdv2010.2 i586

postgresql8.4-docs-8.4.12-0.1mdv2010.2.i586.rpm

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<HTML
><HEAD
><TITLE
>Binary Data Types</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK
REV="MADE"
HREF="mailto:pgsql-docs@postgresql.org"><LINK
REL="HOME"
TITLE="PostgreSQL 8.4.12 Documentation"
HREF="index.html"><LINK
REL="UP"
TITLE="Data Types"
HREF="datatype.html"><LINK
REL="PREVIOUS"
TITLE="Character Types"
HREF="datatype-character.html"><LINK
REL="NEXT"
TITLE="Date/Time Types"
HREF="datatype-datetime.html"><LINK
REL="STYLESHEET"
TYPE="text/css"
HREF="stylesheet.css"><META
HTTP-EQUIV="Content-Type"
CONTENT="text/html; charset=ISO-8859-1"><META
NAME="creation"
CONTENT="2012-05-31T23:30:11"></HEAD
><BODY
CLASS="SECT1"
><DIV
CLASS="NAVHEADER"
><TABLE
SUMMARY="Header navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="5"
ALIGN="center"
VALIGN="bottom"
>PostgreSQL 8.4.12 Documentation</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="top"
><A
HREF="datatype-character.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="top"
><A
HREF="datatype.html"
>Fast Backward</A
></TD
><TD
WIDTH="60%"
ALIGN="center"
VALIGN="bottom"
>Chapter 8. Data Types</TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="top"
><A
HREF="datatype.html"
>Fast Forward</A
></TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="top"
><A
HREF="datatype-datetime.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="DATATYPE-BINARY"
>8.4. Binary Data Types</A
></H1
><A
NAME="AEN4860"
></A
><A
NAME="AEN4862"
></A
><P
>    The <TT
CLASS="TYPE"
>bytea</TT
> data type allows storage of binary strings;
    see <A
HREF="datatype-binary.html#DATATYPE-BINARY-TABLE"
>Table 8-6</A
>.
   </P
><DIV
CLASS="TABLE"
><A
NAME="DATATYPE-BINARY-TABLE"
></A
><P
><B
>Table 8-6. Binary Data Types</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><COL><THEAD
><TR
><TH
>Name</TH
><TH
>Storage Size</TH
><TH
>Description</TH
></TR
></THEAD
><TBODY
><TR
><TD
><TT
CLASS="TYPE"
>bytea</TT
></TD
><TD
>1 or 4 bytes plus the actual binary string</TD
><TD
>variable-length binary string</TD
></TR
></TBODY
></TABLE
></DIV
><P
>    A binary string is a sequence of octets (or bytes).  Binary
    strings are distinguished from character strings in two
    ways: First, binary strings specifically allow storing
    octets of value zero and other <SPAN
CLASS="QUOTE"
>"non-printable"</SPAN
>
    octets (usually, octets outside the range 32 to 126).
    Character strings disallow zero octets, and also disallow any
    other octet values and sequences of octet values that are invalid
    according to the database's selected character set encoding.
    Second, operations on binary strings process the actual bytes,
    whereas the processing of character strings depends on locale settings.
    In short, binary strings are appropriate for storing data that the
    programmer thinks of as <SPAN
CLASS="QUOTE"
>"raw bytes"</SPAN
>, whereas character
    strings are appropriate for storing text.
   </P
><P
>    When entering <TT
CLASS="TYPE"
>bytea</TT
> values, octets of certain
    values <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>must</I
></SPAN
> be escaped (but all octet
    values <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>can</I
></SPAN
> be escaped) when used as part
    of a string literal in an <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> statement. In
    general, to escape an octet, convert it into its three-digit
    octal value and precede it
    by two backslashes.  <A
HREF="datatype-binary.html#DATATYPE-BINARY-SQLESC"
>Table 8-7</A
>
    shows the characters that must be escaped, and gives the alternative
    escape sequences where applicable.
   </P
><DIV
CLASS="TABLE"
><A
NAME="DATATYPE-BINARY-SQLESC"
></A
><P
><B
>Table 8-7. <TT
CLASS="TYPE"
>bytea</TT
> Literal Escaped Octets</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><COL><COL><COL><THEAD
><TR
><TH
>Decimal Octet Value</TH
><TH
>Description</TH
><TH
>Escaped Input Representation</TH
><TH
>Example</TH
><TH
>Output Representation</TH
></TR
></THEAD
><TBODY
><TR
><TD
>0</TD
><TD
>zero octet</TD
><TD
><TT
CLASS="LITERAL"
>E'\\000'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>SELECT E'\\000'::bytea;</TT
></TD
><TD
><TT
CLASS="LITERAL"
>\000</TT
></TD
></TR
><TR
><TD
>39</TD
><TD
>single quote</TD
><TD
><TT
CLASS="LITERAL"
>''''</TT
> or <TT
CLASS="LITERAL"
>E'\\047'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>SELECT E'\''::bytea;</TT
></TD
><TD
><TT
CLASS="LITERAL"
>'</TT
></TD
></TR
><TR
><TD
>92</TD
><TD
>backslash</TD
><TD
><TT
CLASS="LITERAL"
>E'\\\\'</TT
> or <TT
CLASS="LITERAL"
>E'\\134'</TT
></TD
><TD
><TT
CLASS="LITERAL"
>SELECT E'\\\\'::bytea;</TT
></TD
><TD
><TT
CLASS="LITERAL"
>\\</TT
></TD
></TR
><TR
><TD
>0 to 31 and 127 to 255</TD
><TD
><SPAN
CLASS="QUOTE"
>"non-printable"</SPAN
> octets</TD
><TD
><TT
CLASS="LITERAL"
>E'\\<TT
CLASS="REPLACEABLE"
><I
>xxx'</I
></TT
></TT
> (octal value)</TD
><TD
><TT
CLASS="LITERAL"
>SELECT E'\\001'::bytea;</TT
></TD
><TD
><TT
CLASS="LITERAL"
>\001</TT
></TD
></TR
></TBODY
></TABLE
></DIV
><P
>    The requirement to escape <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>non-printable</I
></SPAN
> octets
    varies depending on locale settings. In some instances you can get away
    with leaving them unescaped. Note that the result in each of the examples
    in <A
HREF="datatype-binary.html#DATATYPE-BINARY-SQLESC"
>Table 8-7</A
> was exactly one octet in
    length, even though the output representation is sometimes
    more than one character.
   </P
><P
>    The reason multiple backslashes are required, as shown
    in <A
HREF="datatype-binary.html#DATATYPE-BINARY-SQLESC"
>Table 8-7</A
>, is that an input
    string written as a string literal must pass through two parse
    phases in the <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> server.
    The first backslash of each pair is interpreted as an escape
    character by the string-literal parser (assuming escape string
    syntax is used) and is therefore consumed, leaving the second backslash of the
    pair.  (Dollar-quoted strings can be used to avoid this level
    of escaping.)  The remaining backslash is then recognized by the
    <TT
CLASS="TYPE"
>bytea</TT
> input function as starting either a three
    digit octal value or escaping another backslash.  For example,
    a string literal passed to the server as <TT
CLASS="LITERAL"
>E'\\001'</TT
>
    becomes <TT
CLASS="LITERAL"
>\001</TT
> after passing through the
    escape string parser. The <TT
CLASS="LITERAL"
>\001</TT
> is then sent
    to the <TT
CLASS="TYPE"
>bytea</TT
> input function, where it is converted
    to a single octet with a decimal value of 1.  Note that the
    single-quote character is not treated specially by <TT
CLASS="TYPE"
>bytea</TT
>,
    so it follows the normal rules for string literals.  (See also
    <A
HREF="sql-syntax-lexical.html#SQL-SYNTAX-STRINGS"
>Section 4.1.2.1</A
>.)
   </P
><P
>    <TT
CLASS="TYPE"
>Bytea</TT
> octets are sometimes escaped when output. In general, each
    <SPAN
CLASS="QUOTE"
>"non-printable"</SPAN
> octet is converted into
    its equivalent three-digit octal value and preceded by one backslash.
    Most <SPAN
CLASS="QUOTE"
>"printable"</SPAN
> octets are represented by their standard
    representation in the client character set. The octet with decimal
    value 92 (backslash) is doubled in the output.
    Details are in <A
HREF="datatype-binary.html#DATATYPE-BINARY-RESESC"
>Table 8-8</A
>.
   </P
><DIV
CLASS="TABLE"
><A
NAME="DATATYPE-BINARY-RESESC"
></A
><P
><B
>Table 8-8. <TT
CLASS="TYPE"
>bytea</TT
> Output Escaped Octets</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><COL><COL><COL><THEAD
><TR
><TH
>Decimal Octet Value</TH
><TH
>Description</TH
><TH
>Escaped Output Representation</TH
><TH
>Example</TH
><TH
>Output Result</TH
></TR
></THEAD
><TBODY
><TR
><TD
>92</TD
><TD
>backslash</TD
><TD
><TT
CLASS="LITERAL"
>\\</TT
></TD
><TD
><TT
CLASS="LITERAL"
>SELECT E'\\134'::bytea;</TT
></TD
><TD
><TT
CLASS="LITERAL"
>\\</TT
></TD
></TR
><TR
><TD
>0 to 31 and 127 to 255</TD
><TD
><SPAN
CLASS="QUOTE"
>"non-printable"</SPAN
> octets</TD
><TD
><TT
CLASS="LITERAL"
>\<TT
CLASS="REPLACEABLE"
><I
>xxx</I
></TT
></TT
> (octal value)</TD
><TD
><TT
CLASS="LITERAL"
>SELECT E'\\001'::bytea;</TT
></TD
><TD
><TT
CLASS="LITERAL"
>\001</TT
></TD
></TR
><TR
><TD
>32 to 126</TD
><TD
><SPAN
CLASS="QUOTE"
>"printable"</SPAN
> octets</TD
><TD
>client character set representation</TD
><TD
><TT
CLASS="LITERAL"
>SELECT E'\\176'::bytea;</TT
></TD
><TD
><TT
CLASS="LITERAL"
>~</TT
></TD
></TR
></TBODY
></TABLE
></DIV
><P
>    Depending on the front end to <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> you use,
    you might have additional work to do in terms of escaping and
    unescaping <TT
CLASS="TYPE"
>bytea</TT
> strings. For example, you might also
    have to escape line feeds and carriage returns if your interface
    automatically translates these.
   </P
><P
>        The <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> standard defines a different binary
        string type, called <TT
CLASS="TYPE"
>BLOB</TT
> or <TT
CLASS="TYPE"
>BINARY LARGE
        OBJECT</TT
>.  The input format is different from
        <TT
CLASS="TYPE"
>bytea</TT
>, but the provided functions and operators are
        mostly the same.
   </P
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
SUMMARY="Footer navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="datatype-character.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="index.html"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="datatype-datetime.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Character Types</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="datatype.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>Date/Time Types</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>