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Re: bytea datatype documentation patch

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Joe Conway <joseph(dot)conway(at)home(dot)com>
Cc: "pgsql-patches(at)postgresql(dot)org" <pgsql-patches(at)postgresql(dot)org>
Subject: Re: bytea datatype documentation patch
Date: 2001-11-20 15:42:41
Message-ID: 200111201542.fAKFgfK09271@candle.pha.pa.us (view raw or flat)
Thread:
Lists: pgsql-docspgsql-patches
Patch applied.  Thanks.

---------------------------------------------------------------------------


> Here's a second bytea documentation patch. This one significantly 
> expands the "Binary Data" section added by Bruce recently.
> 
> -- Joe

[ text/html is unsupported, treating like TEXT/PLAIN ]

> *** sgml.orig/datatype.sgml	Mon Nov 19 01:05:00 2001
> --- sgml/datatype.sgml	Tue Nov 20 01:04:54 2001
> ***************
> *** 965,987 ****
>   
>     </sect1>
>   
> !   <sect1 id="datatype-binary">
> !    <title>Binary Data</title>
>   
>      <para>
> !     The <type>bytea</type> data type allows storage of binary data,
> !     specifically allowing storage of NULLs which are entered as
> !     <literal>'\\000'</>. The first backslash is interpreted by the
> !     single quotes, and the second is recognized by <type>bytea</> and
> !     precedes a three digit octal value. For a similar reason, a
> !     backslash must be entered into a field as <literal>'\\\\'</> or
> !     <literal>'\\134'</>. You may also have to escape line feeds and
> !     carriage return if your interface automatically translates these. It
> !     can store values of any length. <type>Bytea</> is a non-standard
> !     data type.
>      </para>
>     </sect1>
>   
>     <sect1 id="datatype-datetime">
>      <title>Date/Time Types</title>
>   
> --- 965,1260 ----
>   
>     </sect1>
>   
> !  <sect1 id="datatype-binary">
> !   <title>Binary Strings</title>
> !    <para>
> !     The <type>bytea</type> data type allows storage of binary strings.
> !    </para>
> ! 
> !    <table tocentry="1">
> !     <title>Binary String Types</title>
> !     <tgroup cols="3">
> !      <thead>
> !       <row>
> !        <entry>Type Name</entry>
> !        <entry>Storage</entry>
> !        <entry>Description</entry>
> !       </row>
> !      </thead>
> !      <tbody>
> !       <row>
> !        <entry>bytea</entry>
> !        <entry>4 bytes plus the actual string</entry>
> !        <entry>Variable (not specifically limited)
> !               length binary string</entry>
> !       </row>
> !      </tbody>
> !     </tgroup>
> !    </table>
> ! 
> !    <para>
> !     A binary string is a sequence of octets that does not have either a
> !     character set or collation associated with it.  Bytea specifically
> !     allows storage of NULLs and other 'non-printable' <acronym>ASCII
> !     </acronym> characters.
> !    </para>
> ! 
> !    <para>
> !     Certain <acronym>ASCII</acronym> characters MUST be escaped (but all
> !     characters MAY be escaped) when used as part of a string literal in an
> !     <acronym>SQL</acronym> statement. In general, to escape a character, it
> !     is converted into the three digit octal number equal to the decimal
> !     <acronym>ASCII</acronym> value, and preceeded by two backslashes. The
> !     single quote (') and backslash (\) characters have special alternate
> !     escape sequences. Details are in
> !     <xref linkend="datatype-binary-sqlesc">.
> !    </para>
> ! 
> !    <table id="datatype-binary-sqlesc">
> !     <title><acronym>SQL</acronym> Literal Escaped <acronym>ASCII</acronym>
> !            Characters</title>
> !     <tgroup cols="5">
> !      <thead>
> !       <row>
> !        <entry>Decimal <acronym>ASCII</acronym> Value</entry>
> !        <entry>Description</entry>
> !        <entry>Input Escaped Representation</entry>
> !        <entry>Example</entry>
> !        <entry>Printed Result</entry>
> !       </row>
> !      </thead>
> ! 
> !      <tbody>
> !       <row>
> !        <entry> <literal> 0 </literal> </entry>
> !        <entry> null byte </entry>
> !        <entry> <literal> '\\000' </literal> </entry>
> !        <entry> <literal> select '\\000'::bytea; </literal> </entry>
> !        <entry> <literal> \000 </literal></entry>
> !       </row>
> ! 
> !       <row>
> !        <entry> <literal> 39 </literal> </entry>
> !        <entry> single quote </entry>
> !        <entry> <literal> '\\'' or '\\047' </literal> </entry>
> !        <entry> <literal> select '\''::bytea; </literal></entry>
> !        <entry> <literal> ' </literal></entry>
> !       </row>
> ! 
> !       <row>
> !        <entry> <literal>92</literal> </entry>
> !        <entry> backslash </entry>
> !        <entry> <literal> '\\\\' or '\\134' </literal> </entry>
> !        <entry> <literal> select '\\\\'::bytea; </literal></entry>
> !        <entry> <literal> \\ </literal></entry>
> !       </row>
> ! 
> !      </tbody>
> !     </tgroup>
> !    </table>
> ! 
> !    <para>
> !     Note that the result in each of the examples above was exactly one
> !     byte in length, even though the output representation of the null byte
> !     and backslash are more than one character. Bytea output characters
> !     are also escaped. In general, each "non-printable" character is
> !     converted into the three digit octal number equal to its decimal
> !     <acronym>ASCII</acronym> value, and preceeded by one backslash. Most
> !     "printable" characters are represented by their standard
> !     <acronym>ASCII</acronym> representation. The backslash (\) character
> !     has a special alternate output representation. Details are in
> !     <xref linkend="datatype-binary-resesc">.
> !    </para>
> ! 
> !    <table id="datatype-binary-resesc">
> !     <title><acronym>SQL</acronym> Output Escaped <acronym>ASCII</acronym>
> !            Characters</title>
> !     <tgroup cols="5">
> !      <thead>
> !       <row>
> !        <entry>Decimal <acronym>ASCII</acronym> Value</entry>
> !        <entry>Description</entry>
> !        <entry>Output Escaped Representation</entry>
> !        <entry>Example</entry>
> !        <entry>Printed Result</entry>
> !       </row>
> !      </thead>
> ! 
> !      <tbody>
> ! 
> !       <row>
> !        <entry> <literal> 39 </literal> </entry>
> !        <entry> single quote </entry>
> !        <entry> <literal> ' </literal> </entry>
> !        <entry> <literal> select '\\047'::bytea; </literal></entry>
> !        <entry> <literal> ' </literal></entry>
> !       </row>
> ! 
> !       <row>
> !        <entry> <literal> 92 </literal> </entry>
> !        <entry> backslash </entry>
> !        <entry> <literal> \\ </literal> </entry>
> !        <entry> <literal> select '\\134'::bytea; </literal></entry>
> !        <entry> <literal> \\ </literal></entry>
> !       </row>
> ! 
> !       <row>
> !        <entry> <literal> 0 to 31 and 127 to 255 </literal> </entry>
> !        <entry> non-printable characters </entry>
> !        <entry> <literal> \### (octal value) </literal> </entry>
> !        <entry> <literal> select '\\001'::bytea; </literal> </entry>
> !        <entry> <literal> \001 </literal></entry>
> !       </row>
> ! 
> !       <row>
> !        <entry> <literal> 32 to 126 </literal> </entry>
> !        <entry> printable characters </entry>
> !        <entry> ASCII representation </entry>
> !        <entry> <literal>  select '\\176'::bytea; </literal> </entry>
> !        <entry> <literal> ~ </literal></entry>
> !       </row>
> ! 
> !      </tbody>
> !     </tgroup>
> !    </table>
> ! 
> !    <para>
> !     <acronym>SQL</acronym> string literals (input strings) must be
> !     preceeded with two backslashes due to the fact that they must pass
> !     through two parsers in the PostgreSQL backend. The first backslash
> !     is interpreted as an escape character by the string literal parser,
> !     and therefore is consumed, leaving the characters that follow it.
> !     The second backslash is recognized by <type>bytea</> input function
> !     as the prefix of a three digit octal value. For example, a string
> !     literal passed to the backend as <literal>'\\001'</literal> becomes
> !     <literal>'\001'</literal> after passing through the string literal
> !     parser. The <literal>'\001'</literal> is then sent to the bytea
> !     input function, where it is converted to a single byte with a decimal
> !     <acronym>ASCII</acronym> value of 1.
> !    </para>
> ! 
> !    <para>
> !     For a similar reason, a backslash must be input as
> !     <literal>'\\\\'</literal> (or <literal>'\\134'</literal>). The first
> !     and third backslashes are interpreted as escape characters by the
> !     string literal parser, and therefore are consumed, leaving the
> !     second and forth backslashes untouched. The second and forth
> !     backslashes are recognized by <type>bytea</> input function as a single
> !     backslash. For example, a string literal passed to the backend as
> !     <literal>'\\\\'</literal> becomes <literal>'\\'</literal> after passing
> !     through the string literal parser. The <literal>'\\'</literal> is then
> !     sent to the bytea input function, where it is converted to a single
> !     byte with a decimal <acronym>ASCII</acronym> value of 92.
> !    </para>
> ! 
> !    <para>
> !     A single quote is a bit different in that it must be input as
> !     <literal>'\''</literal> (or <literal>'\\134'</literal>), NOT as
> !     <literal>'\\''</literal>. This is because, while the literal parser
> !     interprets the single quote as a special character, and will consume
> !     the single backslash, the bytea input function does NOT recognize
> !     a single quote as a special character. Therefore a string
> !     literal passed to the backend as <literal>'\''</literal> becomes
> !     <literal>'''</literal> after passing through the string literal
> !     parser. The <literal>'''</literal> is then sent to the bytea
> !     input function, where it is retains its single byte decimal
> !     <acronym>ASCII</acronym> value of 39.
> !    </para>
>   
>      <para>
> !     Depending on the front end to PostgreSQL you use, you may have
> !     additional work to do in terms of escaping and unescaping bytea
> !     strings. For example, you may also have to escape line feeds and
> !     carriage return if your interface automatically translates these.
> !     Or you may have to double up on backslashes if the parser for your
> !     language or choice also treats them as an escape character.
>      </para>
> + 
> +    <sect2 id="datatype-binary-compat">
> +     <title>Compatibility</title>
> +     <para>
> +      Bytea provides most of the functionality of the SQL99 binary string
> +      type per SQL99 section 4.3. A comparison of PostgreSQL bytea and SQL99
> +      Binary Strings is presented in
> +      <xref linkend="datatype-binary-compat-comp">.
> +     </para>
> + 
> +     <table id="datatype-binary-compat-comp">
> +      <title>Comparison of SQL99 Binary String and BYTEA types</title>
> +      <tgroup cols="2">
> +       <thead>
> +        <row>
> +         <entry>SQL99</entry>
> +         <entry>BYTEA</entry>
> +        </row>
> +       </thead>
> + 
> +       <tbody>
> +        <row>
> +         <entry> Name of data type BINARY LARGE OBJECT or BLOB </entry>
> +         <entry> Name of data type BYTEA </entry>
> +        </row>
> + 
> +        <row>
> +         <entry> Sequence of octets that does not have either a character set
> +                 or collation associated with it. </entry>
> +         <entry> same </entry>
> +        </row>
> + 
> +        <row>
> +         <entry> Described by a binary data type descriptor containing the
> +                 name of the data type and the maximum length
> +                 in octets</entry>
> +         <entry> Described by a binary data type descriptor containing the
> +                 name of the data type with no specific maximum length
> +                 </entry>
> +        </row>
> + 
> +        <row>
> +         <entry> All binary strings are mutually comparable in accordance
> +                 with the rules of comparison predicates.</entry>
> +         <entry> same</entry>
> +        </row>
> + 
> +        <row>
> +         <entry> Binary string values can only be compared for equality.
> +                 </entry>
> +         <entry> Binary string values can be compared for equality, greater
> +                 than, greater than or equal, less than, less than or equal
> +                 </entry>
> +        </row>
> + 
> +        <row>
> +         <entry> Operators operating on and returning binary strings
> +                 include concatenation, substring, overlay, and trim</entry>
> +         <entry> Operators operating on and returning binary strings
> +                 include concatenation, substring, and trim. The <literal>
> +                 'leading'</literal> and <literal>'trailing'</literal>
> +                 arguments for trim are not yet implemented.
> +                 </entry>
> +        </row>
> + 
> +        <row>
> +         <entry> Other operators involving binary strings
> +                 include length, position, and the like predicate</entry>
> +         <entry> same</entry>
> +        </row>
> + 
> +        <row>
> +         <entry> A binary string literal is comprised of an even number of
> +                 hexidecimal digits, in single quotes, preceeded by "X",
> +                 e.g. X'1a43fe'</entry>
> +         <entry> A binary string literal is comprised of ASCII characters
> +                 escaped according to the rules shown in 
> +                 <xref linkend="datatype-binary-sqlesc"> </entry>
> +        </row>
> +       </tbody>
> +      </tgroup>
> +     </table>
> +    </sect2>
>     </sect1>
>   
> + 
>     <sect1 id="datatype-datetime">
>      <title>Date/Time Types</title>
>   

> 
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-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman(at)candle(dot)pha(dot)pa(dot)us               |  (610) 853-3000
  +  If your life is a hard drive,     |  830 Blythe Avenue
  +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026

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