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+$Header: /cvsroot/pgsql/doc/src/sgml/datatype.sgml,v 1.72 2001/11/20 15:42:44 momjian Exp $
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<chapter id="datatype">
</sect1>
- <sect1 id="datatype-binary">
- <title>Binary Data</title>
+ <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>
- 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.
+ 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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+$Header: /cvsroot/pgsql/doc/src/sgml/func.sgml,v 1.83 2001/11/20 15:42:44 momjian Exp $
Postgres documentation
-->
<entry><type>text</type></entry>
<entry>
Encodes binary data to <acronym>ASCII</acronym>-only representation. Supported
- types are: 'base64', 'hex'.
+ types are: 'base64', 'hex', 'escape'.
</entry>
<entry><literal>encode('123\\000\\001', 'base64')</literal></entry>
<entry><literal>MTIzAAE=</literal></entry>
</sect1>
+ <sect1 id="functions-binarystring">
+ <title>Binary String Functions and Operators</title>
+
+ <para>
+ This section describes functions and operators for examining and
+ manipulating binary string values. Strings in this context include
+ values of the type <type>BYTEA</type>.
+ </para>
+
+ <para>
+ <acronym>SQL</acronym> defines some string functions with a special syntax where
+ certain keywords rather than commas are used to separate the
+ arguments. Details are in <xref linkend="functions-binarystring-sql">.
+ Some functions are also implemented using the regular syntax for
+ function invocation. (See <xref linkend="functions-binarystring-other">.)
+ </para>
+
+ <table id="functions-binarystring-sql">
+ <title><acronym>SQL</acronym> Binary String Functions and Operators</title>
+ <tgroup cols="5">
+ <thead>
+ <row>
+ <entry>Function</entry>
+ <entry>Return Type</entry>
+ <entry>Description</entry>
+ <entry>Example</entry>
+ <entry>Result</entry>
+ </row>
+ </thead>
+
+ <tbody>
+ <row>
+ <entry> <parameter>string</parameter> <literal>||</literal> <parameter>string</parameter> </entry>
+ <entry> <type>bytea</type> </entry>
+ <entry>
+ string concatenation
+ <indexterm>
+ <primary>binary strings</primary>
+ <secondary>concatenation</secondary>
+ </indexterm>
+ </entry>
+ <entry><literal>'\\\\Postgre'::bytea || '\\047SQL\\000'::bytea</></entry>
+ <entry><literal>\\Postgre'SQL\000</></entry>
+ </row>
+
+ <row>
+ <entry><function>octet_length</function>(<parameter>string</parameter>)</entry>
+ <entry><type>integer</type></entry>
+ <entry>number of bytes in binary string</entry>
+ <entry><literal>octet_length('jo\\000se'::bytea)</literal></entry>
+ <entry><literal>5</literal></entry>
+ </row>
+
+ <row>
+ <entry><function>position</function>(<parameter>substring</parameter> in <parameter>string</parameter>)</entry>
+ <entry><type>integer</type></entry>
+ <entry>location of specified substring</entry>
+ <entry><literal>position('\\000om'::bytea in 'Th\\000omas'::bytea)</literal></entry>
+ <entry><literal>3</literal></entry>
+ </row>
+
+ <row>
+ <entry><function>substring</function>(<parameter>string</parameter> <optional>from <type>integer</type></optional> <optional>for <type>integer</type></optional>)</entry>
+ <entry><type>bytea</type></entry>
+ <entry>
+ extract substring
+ <indexterm>
+ <primary>substring</primary>
+ </indexterm>
+ </entry>
+ <entry><literal>substring('Th\\000omas'::bytea from 2 for 3)</literal></entry>
+ <entry><literal>h\000o</literal></entry>
+ </row>
+
+ <row>
+ <entry>
+ <function>trim</function>(<optional>both</optional>
+ <parameter>characters</parameter> from
+ <parameter>string</parameter>)
+ </entry>
+ <entry><type>bytea</type></entry>
+ <entry>
+ Removes the longest string containing only the
+ <parameter>characters</parameter> from the
+ beginning/end/both ends of the <parameter>string</parameter>.
+ </entry>
+ <entry><literal>trim('\\000'::bytea from '\\000Tom\\000'::bytea)</literal></entry>
+ <entry><literal>Tom</literal></entry>
+ </row>
+
+ </tbody>
+ </tgroup>
+ </table>
+
+ <para>
+ Additional binary string manipulation functions are available and are
+ listed below. Some of them are used internally to implement the
+ <acronym>SQL</acronym>-standard string functions listed above.
+ </para>
+
+ <table id="functions-binarystring-other">
+ <title>Other Binary String Functions</title>
+ <tgroup cols="5">
+ <thead>
+ <row>
+ <entry>Function</entry>
+ <entry>Return Type</entry>
+ <entry>Description</entry>
+ <entry>Example</entry>
+ <entry>Result</entry>
+ </row>
+ </thead>
+
+ <tbody>
+ <row>
+ <entry><function>btrim</function>(<parameter>string</parameter> <type>bytea</type>, <parameter>trim</parameter> <type>bytea</type>)</entry>
+ <entry><type>bytea</type></entry>
+ <entry>
+ Remove (trim) the longest string consisting only of characters
+ in <parameter>trim</parameter> from the start and end of
+ <parameter>string</parameter>.
+ </entry>
+ <entry><literal>btrim('\\000trim\\000'::bytea,'\\000'::bytea)</literal></entry>
+ <entry><literal>trim</literal></entry>
+ </row>
+
+ <row>
+ <entry><function>length</function>(<parameter>string</parameter>)</entry>
+ <entry><type>integer</type></entry>
+ <entry>
+ length of binary string
+ <indexterm>
+ <primary>binary strings</primary>
+ <secondary>length</secondary>
+ </indexterm>
+ <indexterm>
+ <primary>length</primary>
+ <secondary>binary strings</secondary>
+ <see>binary strings, length</see>
+ </indexterm>
+ </entry>
+ <entry><literal>length('jo\\000se'::bytea)</></entry>
+ <entry><literal>5</></entry>
+ </row>
+
+ <row>
+ <entry>
+ <function>encode</function>(<parameter>string</parameter> <type>bytea</type>,
+ <parameter>type</parameter> <type>text</type>)
+ </entry>
+ <entry><type>text</type></entry>
+ <entry>
+ Encodes binary string to <acronym>ASCII</acronym>-only representation. Supported
+ types are: 'base64', 'hex', 'escape'.
+ </entry>
+ <entry><literal>encode('123\\000456'::bytea, 'escape')</literal></entry>
+ <entry><literal>123\000456</literal></entry>
+ </row>
+
+ <row>
+ <entry>
+ <function>decode</function>(<parameter>string</parameter> <type>text</type>,
+ <parameter>type</parameter> <type>text</type>)
+ </entry>
+ <entry><type>bytea</type></entry>
+ <entry>
+ Decodes binary string from <parameter>string</parameter> previously
+ encoded with encode(). Parameter type is same as in encode().
+ </entry>
+ <entry><literal>decode('123\\000456', 'escape')</literal></entry>
+ <entry><literal>123\000456</literal></entry>
+ </row>
+
+ </tbody>
+ </tgroup>
+ </table>
+
+ </sect1>
+
+
<sect1 id="functions-matching">
<title>Pattern Matching</title>
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