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-$Header: /cvsroot/pgsql/doc/src/sgml/datatype.sgml,v 1.46 2000/12/22 18:57:49 petere Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/datatype.sgml,v 1.47 2001/01/13 18:34:51 petere Exp $
-->
<chapter id="datatype">
<title id="datatype-title">Data Types</title>
- <abstract>
- <para>
- Describes the built-in data types available in
- <productname>Postgres</productname>.
- </para>
- </abstract>
-
<para>
<productname>Postgres</productname> has a rich set of native data
types available to users.
</para>
<para>
- In the context of data types, the following sections will discuss
- <acronym>SQL</acronym> standards compliance, porting issues, and usage.
-
- Some <productname>Postgres</productname> types correspond directly to
- <acronym>SQL92</acronym>-compatible types. In other
- cases, data types defined by <acronym>SQL92</acronym> syntax are mapped directly
- into native <productname>Postgres</productname> types.
-
- Many of the built-in types have obvious external formats. However, several
- types are either unique to <productname>Postgres</productname>,
- such as open and closed paths, or have
- several possibilities for formats, such as the date and time types.
+ <xref linkend="datatype-table"> shows all general-purpose data types
+ available to users. Most of the alternative names listed in the
+ <quote>Aliases</quote> column are the names used internally by
+ <productname>Postgres</productname> for historical reasons. In
+ addition, some internally used or deprecated types are available,
+ but they are not documented here. Many of the built-in types have
+ obvious external formats. However, several types are either unique
+ to <productname>Postgres</productname>, such as open and closed
+ paths, or have several possibilities for formats, such as the date
+ and time types.
</para>
<para>
- <table tocentry="1">
+ <table id="datatype-table">
<title><productname>Postgres</productname> Data Types</title>
<titleabbrev>Data Types</titleabbrev>
<tgroup cols="3">
<thead>
<row>
- <entry><productname>Postgres</productname> Type</entry>
- <entry><acronym>SQL92</acronym> or <acronym>SQL99</acronym> Type</entry>
+ <entry>Type Name</entry>
+ <entry>Aliases</entry>
<entry>Description</entry>
</row>
</thead>
+
<tbody>
<row>
- <entry>bool</entry>
- <entry>boolean</entry>
- <entry>logical boolean (true/false)</entry>
+ <entry><type>bigint</type></entry>
+ <entry><type>int8</type></entry>
+ <entry>signed eight-byte integer</entry>
</row>
+
<row>
- <entry>box</entry>
+ <entry><type>bit</type></entry>
<entry></entry>
- <entry>rectangular box in 2D plane</entry>
+ <entry>fixed-length bit string</entry>
</row>
+
<row>
- <entry>char(n)</entry>
- <entry>character(n)</entry>
- <entry>fixed-length character string</entry>
+ <entry><type>bit varying(<replaceable>n</replaceable>)</type></entry>
+ <entry><type>varbit(<replaceable>n</replaceable>)</type></entry>
+ <entry>variable-length bit string</entry>
</row>
+
<row>
- <entry>cidr</entry>
- <entry></entry>
- <entry>IP network address</entry>
+ <entry><type>boolean</type></entry>
+ <entry><type>bool</type></entry>
+ <entry>logical boolean (true/false)</entry>
</row>
+
<row>
- <entry>circle</entry>
+ <entry><type>box</type></entry>
<entry></entry>
- <entry>circle in 2D plane</entry>
+ <entry>rectangular box in 2D plane</entry>
</row>
+
<row>
- <entry>date</entry>
- <entry>date</entry>
- <entry>calendar date without time of day</entry>
+ <entry><type>character(<replaceable>n</replaceable>)</type></entry>
+ <entry><type>char(<replaceable>n</replaceable>)</type></entry>
+ <entry>fixed-length character string</entry>
</row>
+
<row>
- <entry>decimal</entry>
- <entry>decimal(p,s)</entry>
- <entry>exact numeric with selectable precision</entry>
+ <entry><type>character varying(<replaceable>n</replaceable>)</type></entry>
+ <entry><type>varchar(<replaceable>n</replaceable>)</type></entry>
+ <entry>variable-length character string</entry>
</row>
+
<row>
- <entry>float4</entry>
- <entry>float(<replaceable>p</replaceable>), <replaceable>p</replaceable> < 7</entry>
- <entry>floating-point number with precision <replaceable>p</replaceable></entry>
+ <entry><type>cidr</type></entry>
+ <entry></entry>
+ <entry>IP network address</entry>
</row>
+
<row>
- <entry>float8</entry>
- <entry>float(<replaceable>p</replaceable>), 7 <= <replaceable>p</replaceable> < 16</entry>
- <entry>floating-point number with precision <replaceable>p</replaceable></entry>
+ <entry><type>circle</type></entry>
+ <entry></entry>
+ <entry>circle in 2D plane</entry>
</row>
+
<row>
- <entry>inet</entry>
+ <entry><type>date</type></entry>
<entry></entry>
- <entry>IP network or host address</entry>
+ <entry>calendar date (year, month, day)</entry>
</row>
+
<row>
- <entry>int2</entry>
- <entry>smallint</entry>
- <entry>signed two-byte integer</entry>
+ <entry><type>double precision</type></entry>
+ <entry><type>float8</type></entry>
+ <entry>double precision floating-point number</entry>
</row>
+
<row>
- <entry>int4</entry>
- <entry>int, integer</entry>
- <entry>signed 4-byte integer</entry>
+ <entry><type>inet</type></entry>
+ <entry></entry>
+ <entry>IP host address</entry>
</row>
+
<row>
- <entry>int8</entry>
- <entry></entry>
- <entry>signed 8-byte integer</entry>
+ <entry><type>integer</type></entry>
+ <entry><type>int</type>, <type>int4</type></entry>
+ <entry>signed four-byte integer</entry>
</row>
+
<row>
- <entry>interval</entry>
- <entry>interval</entry>
+ <entry><type>interval</type></entry>
+ <entry></entry>
<entry>general-use time span</entry>
</row>
+
<row>
- <entry>line</entry>
+ <entry><type>line</type></entry>
<entry></entry>
<entry>infinite line in 2D plane</entry>
</row>
+
<row>
- <entry>lseg</entry>
+ <entry><type>lseg</type></entry>
<entry></entry>
<entry>line segment in 2D plane</entry>
</row>
+
<row>
- <entry>money</entry>
- <entry>decimal(9,2)</entry>
- <entry>US-style currency</entry>
+ <entry><type>macaddr</type></entry>
+ <entry></entry>
+ <entry>MAC address</entry>
</row>
+
<row>
- <entry>numeric</entry>
- <entry>numeric(p,s)</entry>
- <entry>exact numeric with selectable precision</entry>
+ <entry><type>money</type></entry>
+ <entry></entry>
+ <entry>US-style currency</entry>
</row>
+
<row>
- <entry>path</entry>
- <entry></entry>
- <entry>open and closed geometric path in 2D plane</entry>
+ <entry><type>numeric(<replaceable>p</replaceable>, <replaceable>s</replaceable>)</type></entry>
+ <entry><type>decimal(<replaceable>p</replaceable>, <replaceable>s</replaceable>)</type></entry>
+ <entry>exact numeric with selectable precision</entry>
</row>
+
<row>
- <entry>point</entry>
+ <entry><type>oid</type></entry>
<entry></entry>
- <entry>geometric point in 2D plane</entry>
+ <entry>object identifier</entry>
</row>
+
<row>
- <entry>polygon</entry>
+ <entry><type>path</type></entry>
<entry></entry>
- <entry>closed geometric path in 2D plane</entry>
+ <entry>open and closed geometric path in 2D plane</entry>
</row>
+
<row>
- <entry>serial</entry>
+ <entry><type>point</type></entry>
<entry></entry>
- <entry>unique id for indexing and cross-reference</entry>
+ <entry>geometric point in 2D plane</entry>
</row>
+
<row>
- <entry>text</entry>
+ <entry><type>polygon</type></entry>
<entry></entry>
- <entry>variable-length character string</entry>
+ <entry>closed geometric path in 2D plane</entry>
</row>
+
<row>
- <entry>time</entry>
- <entry>time [ without time zone ]</entry>
- <entry>time of day</entry>
+ <entry><type>real</type></entry>
+ <entry><type>float4</type></entry>
+ <entry>single precision floating-point number</entry>
</row>
+
<row>
- <entry>timetz</entry>
- <entry>time with time zone</entry>
- <entry>time of day, including time zone</entry>
+ <entry><type>smallint</type></entry>
+ <entry><type>int2</type></entry>
+ <entry>signed two-byte integer</entry>
</row>
+
<row>
- <entry>timestamp</entry>
- <entry>timestamp [ with time zone ]</entry>
- <entry>date/time</entry>
+ <entry><type>serial</type></entry>
+ <entry></entry>
+ <entry>autoincrementing four-byte integer</entry>
</row>
+
<row>
- <entry>varchar(n)</entry>
- <entry>character varying(n)</entry>
+ <entry><type>text</type></entry>
+ <entry></entry>
<entry>variable-length character string</entry>
</row>
- </tbody>
- </tgroup>
- </table>
- </para>
-
- <para>
- <note>
- <para>
- The <type>cidr</type> and <type>inet</type> types are designed to handle any IP type
- but only ipv4 is handled in the current implementation.
- Everything here that talks about ipv4 will apply to ipv6 in a
- future release.
- </para>
- </note>
- </para>
- <para>
- <table tocentry="1">
- <title><productname>Postgres</productname> Function Constants</title>
- <titleabbrev>Constants</titleabbrev>
- <tgroup cols="3">
- <thead>
<row>
- <entry><productname>Postgres</productname> Function</entry>
- <entry><acronym>SQL92</acronym> Constant</entry>
- <entry>Description</entry>
- </row>
- </thead>
- <tbody>
- <row>
- <entry>date('now')</entry>
- <entry>current_date</entry>
- <entry>date of current transaction</entry>
+ <entry><type>time [ without time zone ]</type></entry>
+ <entry></entry>
+ <entry>time of day</entry>
</row>
+
<row>
- <entry>time('now')</entry>
- <entry>current_time</entry>
- <entry>time of current transaction</entry>
+ <entry><type>time with time zone</type></entry>
+ <entry></entry>
+ <entry>time of day, including time zone</entry>
</row>
+
<row>
- <entry>timestamp('now')</entry>
- <entry>current_timestamp</entry>
- <entry>date and time of current transaction</entry>
+ <entry><type>timestamp [ with time zone ]</type></entry>
+ <entry></entry>
+ <entry>date and time</entry>
</row>
</tbody>
</tgroup>
</table>
</para>
- <para>
- <productname>Postgres</productname> has features at the forefront of
- <acronym>ORDBMS</acronym> development. In addition to
- <acronym>SQL99</acronym> conformance, substantial portions
- of <acronym>SQL92</acronym> are also supported.
- Although we strive for <acronym>SQL92</acronym> compliance,
- there are some aspects of the standard
- that are ill considered and which should not live through subsequent standards.
- <productname>Postgres</productname> will not make great efforts to
- conform to these features; however, these tend to apply in little-used
- or obsure cases, and a typical user is not likely to run into them.
- </para>
+ <note>
+ <title>Compatibility</title>
+ <para>
+ The following types (or spellings thereof) are specified by SQL:
+ <type>bit</type>, <type>bit varying</type>, <type>boolean</type>,
+ <type>char</type>, <type>character</type>, <type>character
+ varying</type>, <type>varchar</type>, <type>date</type>,
+ <type>double precision</type>, <type>integer</type>,
+ <type>interval</type>, <type>numeric</type>, <type>decimal</type>,
+ <type>real</type>, <type>smallint</type>, <type>time</type>,
+ <type>timestamp</type> (both with or without time zone).
+ </para>
+ </note>
<para>
Most of the input and output functions corresponding to the
Some of the input and output functions are not invertible. That is,
the result of an output function may lose precision when compared to
the original input.
-
- <note>
- <para>
- Floating point numbers are allowed to retain
- most of the intrinsic precision of the type (typically 15 digits for doubles,
- 6 digits for 4-byte floats).
- Other types with underlying floating point fields (e.g. geometric
- types) carry similar precision.
- </para>
- </note>
</para>
- <sect1 id="numeric-types">
+ <sect1 id="datatype-numeric">
<title>Numeric Types</title>
<para>
<entry>Range</entry>
</row>
</thead>
+
<tbody>
<row>
- <entry>decimal</entry>
- <entry>variable</entry>
- <entry>User-specified precision</entry>
- <entry>no limit</entry>
- </row>
- <row>
- <entry>float4</entry>
- <entry>4 bytes</entry>
- <entry>Variable-precision</entry>
- <entry>6 decimal places</entry>
- </row>
- <row>
- <entry>float8</entry>
- <entry>8 bytes</entry>
- <entry>Variable-precision</entry>
- <entry>15 decimal places</entry>
- </row>
- <row>
- <entry>int2</entry>
+ <entry>smallint</entry>
<entry>2 bytes</entry>
<entry>Fixed-precision</entry>
<entry>-32768 to +32767</entry>
</row>
<row>
- <entry>int4</entry>
+ <entry>integer</entry>
<entry>4 bytes</entry>
<entry>Usual choice for fixed-precision</entry>
<entry>-2147483648 to +2147483647</entry>
</row>
<row>
- <entry>int8</entry>
+ <entry>bigint</entry>
<entry>8 bytes</entry>
<entry>Very large range fixed-precision</entry>
- <entry>~18 decimal places</entry>
+ <entry>about 18 decimal places</entry>
+ </row>
+
+ <row>
+ <entry>decimal</entry>
+ <entry>variable</entry>
+ <entry>User-specified precision</entry>
+ <entry>no limit</entry>
</row>
<row>
<entry>numeric</entry>
<entry>User-specified precision</entry>
<entry>no limit</entry>
</row>
+
+ <row>
+ <entry>real</entry>
+ <entry>4 bytes</entry>
+ <entry>Variable-precision</entry>
+ <entry>6 decimal places</entry>
+ </row>
+ <row>
+ <entry>double precision</entry>
+ <entry>8 bytes</entry>
+ <entry>Variable-precision</entry>
+ <entry>15 decimal places</entry>
+ </row>
+
<row>
<entry>serial</entry>
<entry>4 bytes</entry>
</para>
<para>
- The <type>int8</type> type may not be available on all platforms since
+ The <type>bigint</type> type may not be available on all platforms since
it relies on compiler support for eight-byte integers.
</para>
- <sect2>
+ <sect2 id="datatype-serial">
<title>The Serial Type</title>
<para>
</sect2>
</sect1>
- <sect1 id="monetary-types">
+ <sect1 id="datatype-money">
<title>Monetary Type</title>
<note>
</sect1>
- <sect1 id="character-types">
+ <sect1 id="datatype-character">
<title>Character Types</title>
<para>
- <acronym>SQL92</acronym> defines two primary character types:
- <type>char</type> and <type>varchar</type>.
+ <acronym>SQL</acronym> defines two primary character types:
+ <type>character</type> and <type>character varying</type>.
<productname>Postgres</productname> supports these types, in
addition to the more general <type>text</type> type,
- which unlike <type>varchar</type>
+ which unlike <type>character varying</type>
does not require an explicit declared upper
limit on the size of the field.
</para>
</thead>
<tbody>
<row>
- <entry>"char"</entry>
- <entry>1 byte</entry>
- <entry><acronym>SQL92</acronym>-compatible</entry>
- <entry>Single character</entry>
+ <entry>character(n), char(n)</entry>
+ <entry>(4+n) bytes</entry>
+ <entry><acronym>SQL</acronym>-compatible</entry>
+ <entry>Fixed-length blank padded</entry>
</row>
<row>
- <entry>char(n)</entry>
+ <entry>character varying(n), varchar(n)</entry>
<entry>(4+n) bytes</entry>
- <entry><acronym>SQL92</acronym>-compatible</entry>
- <entry>Fixed-length blank padded</entry>
+ <entry><acronym>SQL</acronym>-compatible</entry>
+ <entry>Variable-length with limit</entry>
</row>
<row>
<entry>text</entry>
<entry>Most flexible</entry>
<entry>Variable unlimited length</entry>
</row>
- <row>
- <entry>varchar(n)</entry>
- <entry>(4+n) bytes</entry>
- <entry><acronym>SQL92</acronym>-compatible</entry>
- <entry>Variable-length with limit</entry>
- </row>
</tbody>
</tgroup>
</table>
+
+ <note>
+ <para>
+ Although the type <type>text</type> is not SQL-compliant, many
+ other RDBMS packages have it as well.
+ </para>
+ </note>
</para>
<para>
- There is one other fixed-length character type in <productname>Postgres</productname>.
- The <type>name</type> type exists <emphasis>only</emphasis> for
- storage of internal catalog names and
- is not intended for use by the general user.
- Its length is currently defined as 32 bytes (31 characters plus terminator)
- but should be reference using NAMEDATALEN.
- The length is set at compile time (and is therefore adjustable for
- special uses); the default maximum length may change in a future release.
+ There are two other fixed-length character types in
+ <productname>Postgres</productname>. The <type>name</type> type
+ exists <emphasis>only</emphasis> for storage of internal catalog
+ names and is not intended for use by the general user. Its length
+ is currently defined as 32 bytes (31 characters plus terminator)
+ but should be referenced using the macro
+ <symbol>NAMEDATALEN</symbol>. The length is set at compile time
+ (and is therefore adjustable for special uses); the default
+ maximum length may change in a future release. The type
+ <type>"char"</type> (note the quotes) is different from
+ <type>char(1)</type> in that it only uses one byte of storage. It
+ is internally used in the system catalogs as a poor-man's
+ enumeration type.
</para>
<para>
</thead>
<tbody>
<row>
+ <entry>"char"</entry>
+ <entry>1 byte</entry>
+ <entry>Single character internal type</entry>
+ </row>
+ <row>
<entry>name</entry>
<entry>32 bytes</entry>
<entry>Thirty-one character internal type</entry>
</sect1>
- <sect1 id="datetime-types">
+ <sect1 id="datatype-datetime">
<title>Date/Time Types</title>
<para>
</para>
- <sect2>
+ <sect2 id="datatype-datetime-input">
<title>Date/Time Input</title>
<para>
</para>
<para>
- See <xref endterm="datetime-appendix-title" linkend="datetime-appendix-title">
+ See <xref linkend="datetime-appendix">
for the exact parsing rules of date/time input and for the recognized time zones.
</para>
</para>
<para>
- Refer to <xref endterm="timezone-title" linkend="timezone"> for
+ Refer to <xref linkend="datatype-timezone-table"> for
more examples of time zones.
</para>
</sect3>
</para>
<para>
- <table tocentry="1" id="timezone">
- <title
id="timezone-title"><productname>Postgres</productname> Time Zone Input</title>
+ <table tocentry="1" id="datatype-timezone-table">
+ <title><productname>Postgres</productname> Time Zone Input</title>
<titleabbrev>Time Zone Inputs</titleabbrev>
<tgroup cols="2">
<thead>
</sect2>
- <sect2>
+ <sect2 id="datatype-datetime-output">
<title>Date/Time Output</title>
<para>
</sect2>
- <sect2>
+ <sect2 id="datatype-timezones">
<title>Time Zones</title>
<para>
</sect2>
- <sect2>
+ <sect2 id="datatype-datetime-internals">
<title>Internals</title>
<para>
</sect1>
- <sect1 id="boolean-type">
+ <sect1 id="datatype-boolean">
<title>Boolean Type</title>
<para>
- <productname>Postgres</productname> supports <type>bool</type> as
- the <acronym>SQL99</acronym> boolean type.
- <type>bool</type> can have one of only two states: 'true' or 'false'.
- A third state, 'unknown', is not
- implemented and is not suggested in <acronym>SQL99</acronym>;
- <acronym>NULL</acronym> is an
- effective substitute. <type>bool</type> can be used in any boolean expression,
- and boolean expressions
- always evaluate to a result compatible with this type.</para>
+ <productname>Postgres</productname> supports the
+ <acronym>SQL99</acronym> <type>boolean</type> type.
+ <type>boolean</type> can have one of only two states: 'true' or
+ 'false'. A third state, 'unknown', is represented by the SQL NULL
+ state. <type>boolean</type> can be used in any boolean expression,
+ and boolean expressions always evaluate to a result compatible
+ with this type.
+ </para>
<para>
- <type>bool</type> uses 1 byte of storage.
+ <type>boolean</type> uses 1 byte of storage.
</para>
<para>
</para>
</sect1>
- <sect1 id="geometric-types">
+ <sect1 id="datatype-geometric">
<title>Geometric Types</title>
<para>
</sect1>
- <sect1 id="net-types">
+ <sect1 id="datatype-net-types">
<title>Network Address Data Types</title>
<para>
types, because these types offer input error checking and several
specialized operators and functions.
- <table tocentry="1" id="net-types-table">
+ <table tocentry="1" id="datatype-net-types-table">
<title>Network Address Data Types</title>
<tgroup cols="4">
<thead>
</para>
- <sect2 id="inet-type">
+ <sect2 id="datatype-inet">
<title><type>inet</type></title>
<para>
</para>
</sect2>
- <sect2 id="cidr-type">
+ <sect2 id="datatype-cidr">
<title><type>cidr</></title>
<para>
</para>
</sect2>
- <sect2 id="inet-vs-cidr">
+ <sect2 id="datatype-inet-vs-cidr">
<title><type>inet</type> vs <type>cidr</type></title>
<para>
</para>
</sect2>
- <sect2 id="macaddr-type">
+ <sect2 id="datatype-macaddr">
<title><type>macaddr</></>
<para>
</sect1>
+ <sect1 id="datatype-bit">
+ <title>Bit String Types</title>
+
+ <para>
+ Bit strings are strings of 1's and 0's. They can be used to store
+ or visualize bit masks. There are two SQL bit types:
+ <type>BIT(<replaceable>x</replaceable>)</type> and <type>BIT
+ VARYING(<replaceable>x</replaceable>)</type>; the
+ <replaceable>x</replaceable> specifies the maximum length.
+ <type>BIT</type> type data is automatically padded with 0's on the
+ right to the maximum length, <type>BIT VARYING</type> is of
+ variable length. <type>BIT</type> without length is requivalent
+ to <literal>BIT(1)</literal>, <type>BIT VARYING</type> means
+ unlimited length. Input data that is longer than the allowed
+ length will be truncated. Refer to <xref
+ linkend="sql-syntax-bit-strings"> for information about the syntax
+ of bit string constants. Bit-logical operators and string
+ manipulation functions are available; see <xref
+ linkend="functions">.
+ </para>
+
+ <informalexample>
+ <para>
+ Some examples:
+<programlisting>
+CREATE TABLE test (a BIT(3), b BIT VARYING(5));
+INSERT INTO test VALUES (B'101', B'00');
+SELECT SUBSTRING(b FROM 1 FOR 2) FROM test;
+</programlisting>
+ </para>
+ </informalexample>
+
+ </sect1>
+
</chapter>
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