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<html>
<head>
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<title>Chapter8.Data Types</title>
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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="chapter" lang="en" id="datatype">
<div class="titlepage"><div><div><h2 class="title">
<a name="datatype"></a>Chapter8.Data Types</h2></div></div></div>
<div class="toc">
<p><b>Table of Contents</b></p>
<dl>
<dt><span class="sect1"><a href="datatype.html#datatype-numeric">8.1. Numeric Types</a></span></dt>
<dd><dl>
<dt><span class="sect2"><a href="datatype.html#datatype-int">8.1.1. Integer Types</a></span></dt>
<dt><span class="sect2"><a href="datatype.html#datatype-numeric-decimal">8.1.2. Arbitrary Precision Numbers</a></span></dt>
<dt><span class="sect2"><a href="datatype.html#datatype-float">8.1.3. Floating-Point Types</a></span></dt>
<dt><span class="sect2"><a href="datatype.html#datatype-serial">8.1.4. Serial Types</a></span></dt>
</dl></dd>
<dt><span class="sect1"><a href="datatype-money.html">8.2. Monetary Types</a></span></dt>
<dt><span class="sect1"><a href="datatype-character.html">8.3. Character Types</a></span></dt>
<dt><span class="sect1"><a href="datatype-binary.html">8.4. Binary Data Types</a></span></dt>
<dt><span class="sect1"><a href="datatype-datetime.html">8.5. Date/Time Types</a></span></dt>
<dd><dl>
<dt><span class="sect2"><a href="datatype-datetime.html#datatype-datetime-input">8.5.1. Date/Time Input</a></span></dt>
<dt><span class="sect2"><a href="datatype-datetime.html#datatype-datetime-output">8.5.2. Date/Time Output</a></span></dt>
<dt><span class="sect2"><a href="datatype-datetime.html#datatype-timezones">8.5.3. Time Zones</a></span></dt>
<dt><span class="sect2"><a href="datatype-datetime.html#datatype-datetime-internals">8.5.4. Internals</a></span></dt>
</dl></dd>
<dt><span class="sect1"><a href="datatype-boolean.html">8.6. Boolean Type</a></span></dt>
<dt><span class="sect1"><a href="datatype-geometric.html">8.7. Geometric Types</a></span></dt>
<dd><dl>
<dt><span class="sect2"><a href="datatype-geometric.html#id589831">8.7.1. Points</a></span></dt>
<dt><span class="sect2"><a href="datatype-geometric.html#id589880">8.7.2. Line Segments</a></span></dt>
<dt><span class="sect2"><a href="datatype-geometric.html#id589988">8.7.3. Boxes</a></span></dt>
<dt><span class="sect2"><a href="datatype-geometric.html#id590100">8.7.4. Paths</a></span></dt>
<dt><span class="sect2"><a href="datatype-geometric.html#id590235">8.7.5. Polygons</a></span></dt>
<dt><span class="sect2"><a href="datatype-geometric.html#id590332">8.7.6. Circles</a></span></dt>
</dl></dd>
<dt><span class="sect1"><a href="datatype-net-types.html">8.8. Network Address Types</a></span></dt>
<dd><dl>
<dt><span class="sect2"><a href="datatype-net-types.html#datatype-inet">8.8.1. <code class="type">inet</code></a></span></dt>
<dt><span class="sect2"><a href="datatype-net-types.html#datatype-cidr">8.8.2. <code class="type">cidr</code></a></span></dt>
<dt><span class="sect2"><a href="datatype-net-types.html#datatype-inet-vs-cidr">8.8.3. <code class="type">inet</code> vs. <code class="type">cidr</code></a></span></dt>
<dt><span class="sect2"><a href="datatype-net-types.html#datatype-macaddr">8.8.4. <code class="type">macaddr</code></a></span></dt>
</dl></dd>
<dt><span class="sect1"><a href="datatype-bit.html">8.9. Bit String Types</a></span></dt>
<dt><span class="sect1"><a href="arrays.html">8.10. Arrays</a></span></dt>
<dd><dl>
<dt><span class="sect2"><a href="arrays.html#id591292">8.10.1. Declaration of Array Types</a></span></dt>
<dt><span class="sect2"><a href="arrays.html#id591410">8.10.2. Array Value Input</a></span></dt>
<dt><span class="sect2"><a href="arrays.html#id591619">8.10.3. Accessing Arrays</a></span></dt>
<dt><span class="sect2"><a href="arrays.html#id591827">8.10.4. Modifying Arrays</a></span></dt>
<dt><span class="sect2"><a href="arrays.html#id592063">8.10.5. Searching in Arrays</a></span></dt>
<dt><span class="sect2"><a href="arrays.html#id592118">8.10.6. Array Input and Output Syntax</a></span></dt>
</dl></dd>
<dt><span class="sect1"><a href="rowtypes.html">8.11. Composite Types</a></span></dt>
<dd><dl>
<dt><span class="sect2"><a href="rowtypes.html#id592411">8.11.1. Declaration of Composite Types</a></span></dt>
<dt><span class="sect2"><a href="rowtypes.html#id592516">8.11.2. Composite Value Input</a></span></dt>
<dt><span class="sect2"><a href="rowtypes.html#id592645">8.11.3. Accessing Composite Types</a></span></dt>
<dt><span class="sect2"><a href="rowtypes.html#id592723">8.11.4. Modifying Composite Types</a></span></dt>
<dt><span class="sect2"><a href="rowtypes.html#id592789">8.11.5. Composite Type Input and Output Syntax</a></span></dt>
</dl></dd>
<dt><span class="sect1"><a href="datatype-oid.html">8.12. Object Identifier Types</a></span></dt>
<dt><span class="sect1"><a href="datatype-pseudo.html">8.13. Pseudo-Types</a></span></dt>
</dl>
</div>
<a name="id583611"></a><a name="id583621"></a><p> <span class="productname">PostgreSQL</span> has a rich set of native data
types available to users. Users may add new types to
<span class="productname">PostgreSQL</span> using the <a href="sql-createtype.html">CREATE TYPE</a> command.
</p>
<p> <a href="datatype.html#datatype-table" title="Table8.1.Data Types">Table8.1, “Data Types”</a> shows all the built-in general-purpose data
types. Most of the alternative names listed in the
“<span class="quote">Aliases</span>” column are the names used internally by
<span class="productname">PostgreSQL</span> for historical reasons. In
addition, some internally used or deprecated types are available,
but they are not listed here.
</p>
<div class="table">
<a name="datatype-table"></a><p class="title"><b>Table8.1.Data Types</b></p>
<div class="table-contents"><table summary="Data Types" border="1">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>Name</th>
<th>Aliases</th>
<th>Description</th>
</tr></thead>
<tbody>
<tr>
<td><code class="type">bigint</code></td>
<td><code class="type">int8</code></td>
<td>signed eight-byte integer</td>
</tr>
<tr>
<td><code class="type">bigserial</code></td>
<td><code class="type">serial8</code></td>
<td>autoincrementing eight-byte integer</td>
</tr>
<tr>
<td><code class="type">bit [ (<em class="replaceable"><code>n</code></em>) ]</code></td>
<td></td>
<td>fixed-length bit string</td>
</tr>
<tr>
<td><code class="type">bit varying [ (<em class="replaceable"><code>n</code></em>) ]</code></td>
<td><code class="type">varbit</code></td>
<td>variable-length bit string</td>
</tr>
<tr>
<td><code class="type">boolean</code></td>
<td><code class="type">bool</code></td>
<td>logical Boolean (true/false)</td>
</tr>
<tr>
<td><code class="type">box</code></td>
<td></td>
<td>rectangular box in the plane</td>
</tr>
<tr>
<td><code class="type">bytea</code></td>
<td></td>
<td>binary data (“<span class="quote">byte array</span>”)</td>
</tr>
<tr>
<td><code class="type">character varying [ (<em class="replaceable"><code>n</code></em>) ]</code></td>
<td><code class="type">varchar [ (<em class="replaceable"><code>n</code></em>) ]</code></td>
<td>variable-length character string</td>
</tr>
<tr>
<td><code class="type">character [ (<em class="replaceable"><code>n</code></em>) ]</code></td>
<td><code class="type">char [ (<em class="replaceable"><code>n</code></em>) ]</code></td>
<td>fixed-length character string</td>
</tr>
<tr>
<td><code class="type">cidr</code></td>
<td></td>
<td>IPv4 or IPv6 network address</td>
</tr>
<tr>
<td><code class="type">circle</code></td>
<td></td>
<td>circle in the plane</td>
</tr>
<tr>
<td><code class="type">date</code></td>
<td></td>
<td>calendar date (year, month, day)</td>
</tr>
<tr>
<td><code class="type">double precision</code></td>
<td><code class="type">float8</code></td>
<td>double precision floating-point number</td>
</tr>
<tr>
<td><code class="type">inet</code></td>
<td></td>
<td>IPv4 or IPv6 host address</td>
</tr>
<tr>
<td><code class="type">integer</code></td>
<td>
<code class="type">int</code>, <code class="type">int4</code>
</td>
<td>signed four-byte integer</td>
</tr>
<tr>
<td><code class="type">interval [ (<em class="replaceable"><code>p</code></em>) ]</code></td>
<td></td>
<td>time span</td>
</tr>
<tr>
<td><code class="type">line</code></td>
<td></td>
<td>infinite line in the plane</td>
</tr>
<tr>
<td><code class="type">lseg</code></td>
<td></td>
<td>line segment in the plane</td>
</tr>
<tr>
<td><code class="type">macaddr</code></td>
<td></td>
<td>MAC address</td>
</tr>
<tr>
<td><code class="type">money</code></td>
<td></td>
<td>currency amount</td>
</tr>
<tr>
<td><code class="type">numeric [ (<em class="replaceable"><code>p</code></em>,
<em class="replaceable"><code>s</code></em>) ]</code></td>
<td><code class="type">decimal [ (<em class="replaceable"><code>p</code></em>,
<em class="replaceable"><code>s</code></em>) ]</code></td>
<td>exact numeric of selectable precision</td>
</tr>
<tr>
<td><code class="type">path</code></td>
<td></td>
<td>geometric path in the plane</td>
</tr>
<tr>
<td><code class="type">point</code></td>
<td></td>
<td>geometric point in the plane</td>
</tr>
<tr>
<td><code class="type">polygon</code></td>
<td></td>
<td>closed geometric path in the plane</td>
</tr>
<tr>
<td><code class="type">real</code></td>
<td><code class="type">float4</code></td>
<td>single precision floating-point number</td>
</tr>
<tr>
<td><code class="type">smallint</code></td>
<td><code class="type">int2</code></td>
<td>signed two-byte integer</td>
</tr>
<tr>
<td><code class="type">serial</code></td>
<td><code class="type">serial4</code></td>
<td>autoincrementing four-byte integer</td>
</tr>
<tr>
<td><code class="type">text</code></td>
<td></td>
<td>variable-length character string</td>
</tr>
<tr>
<td><code class="type">time [ (<em class="replaceable"><code>p</code></em>) ] [ without time zone ]</code></td>
<td></td>
<td>time of day</td>
</tr>
<tr>
<td><code class="type">time [ (<em class="replaceable"><code>p</code></em>) ] with time zone</code></td>
<td><code class="type">timetz</code></td>
<td>time of day, including time zone</td>
</tr>
<tr>
<td><code class="type">timestamp [ (<em class="replaceable"><code>p</code></em>) ] [ without time zone ]</code></td>
<td></td>
<td>date and time</td>
</tr>
<tr>
<td><code class="type">timestamp [ (<em class="replaceable"><code>p</code></em>) ] with time zone</code></td>
<td><code class="type">timestamptz</code></td>
<td>date and time, including time zone</td>
</tr>
</tbody>
</table></div>
</div>
<br class="table-break"><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Compatibility</h3>
<p> The following types (or spellings thereof) are specified by
<acronym class="acronym">SQL</acronym>: <code class="type">bit</code>, <code class="type">bit
varying</code>, <code class="type">boolean</code>, <code class="type">char</code>,
<code class="type">character varying</code>, <code class="type">character</code>,
<code class="type">varchar</code>, <code class="type">date</code>, <code class="type">double
precision</code>, <code class="type">integer</code>, <code class="type">interval</code>,
<code class="type">numeric</code>, <code class="type">decimal</code>, <code class="type">real</code>,
<code class="type">smallint</code>, <code class="type">time</code> (with or without time zone),
<code class="type">timestamp</code> (with or without time zone).
</p>
</div>
<p> Each data type has an external representation determined by its input
and output functions. Many of the built-in types have
obvious external formats. However, several types are either unique
to <span class="productname">PostgreSQL</span>, such as geometric
paths, or have several possibilities for formats, such as the date
and time types.
Some of the input and output functions are not invertible. That is,
the result of an output function may lose accuracy when compared to
the original input.
</p>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="datatype-numeric"></a>8.1.Numeric Types</h2></div></div></div>
<a name="id584220"></a><p> Numeric types consist of two-, four-, and eight-byte integers,
four- and eight-byte floating-point numbers, and selectable-precision
decimals. <a href="datatype.html#datatype-numeric-table" title="Table8.2.Numeric Types">Table8.2, “Numeric Types”</a> lists the
available types.
</p>
<div class="table">
<a name="datatype-numeric-table"></a><p class="title"><b>Table8.2.Numeric Types</b></p>
<div class="table-contents"><table summary="Numeric Types" border="1">
<colgroup>
<col>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>Name</th>
<th>Storage Size</th>
<th>Description</th>
<th>Range</th>
</tr></thead>
<tbody>
<tr>
<td><code class="type">smallint</code></td>
<td>2 bytes</td>
<td>small-range integer</td>
<td>-32768 to +32767</td>
</tr>
<tr>
<td><code class="type">integer</code></td>
<td>4 bytes</td>
<td>usual choice for integer</td>
<td>-2147483648 to +2147483647</td>
</tr>
<tr>
<td><code class="type">bigint</code></td>
<td>8 bytes</td>
<td>large-range integer</td>
<td>-9223372036854775808 to 9223372036854775807</td>
</tr>
<tr>
<td><code class="type">decimal</code></td>
<td>variable</td>
<td>user-specified precision, exact</td>
<td>no limit</td>
</tr>
<tr>
<td><code class="type">numeric</code></td>
<td>variable</td>
<td>user-specified precision, exact</td>
<td>no limit</td>
</tr>
<tr>
<td><code class="type">real</code></td>
<td>4 bytes</td>
<td>variable-precision, inexact</td>
<td>6 decimal digits precision</td>
</tr>
<tr>
<td><code class="type">double precision</code></td>
<td>8 bytes</td>
<td>variable-precision, inexact</td>
<td>15 decimal digits precision</td>
</tr>
<tr>
<td><code class="type">serial</code></td>
<td>4 bytes</td>
<td>autoincrementing integer</td>
<td>1 to 2147483647</td>
</tr>
<tr>
<td><code class="type">bigserial</code></td>
<td>8 bytes</td>
<td>large autoincrementing integer</td>
<td>1 to 9223372036854775807</td>
</tr>
</tbody>
</table></div>
</div>
<br class="table-break"><p> The syntax of constants for the numeric types is described in
<a href="sql-syntax.html#sql-syntax-constants" title="4.1.2.Constants">Section4.1.2, “Constants”</a>. The numeric types have a
full set of corresponding arithmetic operators and
functions. Refer to <a href="functions.html" title="Chapter9.Functions and Operators">Chapter9, <i>Functions and Operators</i></a> for more
information. The following sections describe the types in detail.
</p>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="datatype-int"></a>8.1.1.Integer Types</h3></div></div></div>
<a name="id584428"></a><a name="id584439"></a><a name="id584449"></a><a name="id584460"></a><a name="id584469"></a><a name="id584477"></a><p> The types <code class="type">smallint</code>, <code class="type">integer</code>, and
<code class="type">bigint</code> store whole numbers, that is, numbers without
fractional components, of various ranges. Attempts to store
values outside of the allowed range will result in an error.
</p>
<p> The type <code class="type">integer</code> is the usual choice, as it offers
the best balance between range, storage size, and performance.
The <code class="type">smallint</code> type is generally only used if disk
space is at a premium. The <code class="type">bigint</code> type should only
be used if the <code class="type">integer</code> range is not sufficient,
because the latter is definitely faster.
</p>
<p> The <code class="type">bigint</code> type may not function correctly on all
platforms, since it relies on compiler support for eight-byte
integers. On a machine without such support, <code class="type">bigint</code>
acts the same as <code class="type">integer</code> (but still takes up eight
bytes of storage). However, we are not aware of any reasonable
platform where this is actually the case.
</p>
<p> <acronym class="acronym">SQL</acronym> only specifies the integer types
<code class="type">integer</code> (or <code class="type">int</code>) and
<code class="type">smallint</code>. The type <code class="type">bigint</code>, and the
type names <code class="type">int2</code>, <code class="type">int4</code>, and
<code class="type">int8</code> are extensions, which are shared with various
other <acronym class="acronym">SQL</acronym> database systems.
</p>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="datatype-numeric-decimal"></a>8.1.2.Arbitrary Precision Numbers</h3></div></div></div>
<a name="id584599"></a><a name="id584612"></a><p> The type <code class="type">numeric</code> can store numbers with up to 1000
digits of precision and perform calculations exactly. It is
especially recommended for storing monetary amounts and other
quantities where exactness is required. However, arithmetic on
<code class="type">numeric</code> values is very slow compared to the integer
types, or to the floating-point types described in the next section.
</p>
<p> In what follows we use these terms: The
<em class="firstterm">scale</em> of a <code class="type">numeric</code> is the
count of decimal digits in the fractional part, to the right of
the decimal point. The <em class="firstterm">precision</em> of a
<code class="type">numeric</code> is the total count of significant digits in
the whole number, that is, the number of digits to both sides of
the decimal point. So the number 23.5141 has a precision of 6
and a scale of 4. Integers can be considered to have a scale of
zero.
</p>
<p> Both the maximum precision and the maximum scale of a
<code class="type">numeric</code> column can be
configured. To declare a column of type <code class="type">numeric</code> use
the syntax
</p>
<pre class="programlisting">NUMERIC(<em class="replaceable"><code>precision</code></em>, <em class="replaceable"><code>scale</code></em>)</pre>
<p>
The precision must be positive, the scale zero or positive.
Alternatively,
</p>
<pre class="programlisting">NUMERIC(<em class="replaceable"><code>precision</code></em>)</pre>
<p>
selects a scale of 0. Specifying
</p>
<pre class="programlisting">NUMERIC</pre>
<p>
without any precision or scale creates a column in which numeric
values of any precision and scale can be stored, up to the
implementation limit on precision. A column of this kind will
not coerce input values to any particular scale, whereas
<code class="type">numeric</code> columns with a declared scale will coerce
input values to that scale. (The <acronym class="acronym">SQL</acronym> standard
requires a default scale of 0, i.e., coercion to integer
precision. We find this a bit useless. If you're concerned
about portability, always specify the precision and scale
explicitly.)
</p>
<p> If the scale of a value to be stored is greater than the declared
scale of the column, the system will round the value to the specified
number of fractional digits. Then, if the number of digits to the
left of the decimal point exceeds the declared precision minus the
declared scale, an error is raised.
</p>
<p> Numeric values are physically stored without any extra leading or
trailing zeroes. Thus, the declared precision and scale of a column
are maximums, not fixed allocations. (In this sense the <code class="type">numeric</code>
type is more akin to <code class="type">varchar(<em class="replaceable"><code>n</code></em>)</code>
than to <code class="type">char(<em class="replaceable"><code>n</code></em>)</code>.) The actual storage
requirement is two bytes for each group of four decimal digits,
plus eight bytes overhead.
</p>
<p> In addition to ordinary numeric values, the <code class="type">numeric</code>
type allows the special value <code class="literal">NaN</code>, meaning
“<span class="quote">not-a-number</span>”. Any operation on <code class="literal">NaN</code>
yields another <code class="literal">NaN</code>. When writing this value
as a constant in a SQL command, you must put quotes around it,
for example <code class="literal">UPDATE table SET x = 'NaN'</code>. On input,
the string <code class="literal">NaN</code> is recognized in a case-insensitive manner.
</p>
<p> The types <code class="type">decimal</code> and <code class="type">numeric</code> are
equivalent. Both types are part of the <acronym class="acronym">SQL</acronym>
standard.
</p>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="datatype-float"></a>8.1.3.Floating-Point Types</h3></div></div></div>
<a name="id584838"></a><a name="id584850"></a><a name="id584860"></a><a name="id584869"></a><a name="id584878"></a><p> The data types <code class="type">real</code> and <code class="type">double
precision</code> are inexact, variable-precision numeric types.
In practice, these types are usually implementations of
<acronym class="acronym">IEEE</acronym> Standard 754 for Binary Floating-Point
Arithmetic (single and double precision, respectively), to the
extent that the underlying processor, operating system, and
compiler support it.
</p>
<p> Inexact means that some values cannot be converted exactly to the
internal format and are stored as approximations, so that storing
and printing back out a value may show slight discrepancies.
Managing these errors and how they propagate through calculations
is the subject of an entire branch of mathematics and computer
science and will not be discussed further here, except for the
following points:
</p>
<div class="itemizedlist"><ul type="disc">
<li><p> If you require exact storage and calculations (such as for
monetary amounts), use the <code class="type">numeric</code> type instead.
</p></li>
<li><p> If you want to do complicated calculations with these types
for anything important, especially if you rely on certain
behavior in boundary cases (infinity, underflow), you should
evaluate the implementation carefully.
</p></li>
<li><p> Comparing two floating-point values for equality may or may
not work as expected.
</p></li>
</ul></div>
<p>
</p>
<p> On most platforms, the <code class="type">real</code> type has a range of at least
1E-37 to 1E+37 with a precision of at least 6 decimal digits. The
<code class="type">double precision</code> type typically has a range of around
1E-307 to 1E+308 with a precision of at least 15 digits. Values that
are too large or too small will cause an error. Rounding may
take place if the precision of an input number is too high.
Numbers too close to zero that are not representable as distinct
from zero will cause an underflow error.
</p>
<p> In addition to ordinary numeric values, the floating-point types
have several special values:
</p>
<div class="literallayout"><p><code class="literal">Infinity</code><br>
<code class="literal">-Infinity</code><br>
<code class="literal">NaN</code></p></div>
<p>
These represent the IEEE 754 special values
“<span class="quote">infinity</span>”, “<span class="quote">negative infinity</span>”, and
“<span class="quote">not-a-number</span>”, respectively. (On a machine whose
floating-point arithmetic does not follow IEEE 754, these values
will probably not work as expected.) When writing these values
as constants in a SQL command, you must put quotes around them,
for example <code class="literal">UPDATE table SET x = 'Infinity'</code>. On input,
these strings are recognized in a case-insensitive manner.
</p>
<p> <span class="productname">PostgreSQL</span> also supports the SQL-standard
notations <code class="type">float</code> and
<code class="type">float(<em class="replaceable"><code>p</code></em>)</code> for specifying
inexact numeric types. Here, <em class="replaceable"><code>p</code></em> specifies
the minimum acceptable precision in binary digits.
<span class="productname">PostgreSQL</span> accepts
<code class="type">float(1)</code> to <code class="type">float(24)</code> as selecting the
<code class="type">real</code> type, while
<code class="type">float(25)</code> to <code class="type">float(53)</code> select
<code class="type">double precision</code>. Values of <em class="replaceable"><code>p</code></em>
outside the allowed range draw an error.
<code class="type">float</code> with no precision specified is taken to mean
<code class="type">double precision</code>.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p> Prior to <span class="productname">PostgreSQL</span> 7.4, the precision in
<code class="type">float(<em class="replaceable"><code>p</code></em>)</code> was taken to mean
so many decimal digits. This has been corrected to match the SQL
standard, which specifies that the precision is measured in binary
digits. The assumption that <code class="type">real</code> and
<code class="type">double precision</code> have exactly 24 and 53 bits in the
mantissa respectively is correct for IEEE-standard floating point
implementations. On non-IEEE platforms it may be off a little, but
for simplicity the same ranges of <em class="replaceable"><code>p</code></em> are used
on all platforms.
</p>
</div>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="datatype-serial"></a>8.1.4.Serial Types</h3></div></div></div>
<a name="id585134"></a><a name="id585144"></a><a name="id585154"></a><a name="id585164"></a><a name="id585175"></a><a name="id585183"></a><p> The data types <code class="type">serial</code> and <code class="type">bigserial</code>
are not true types, but merely
a notational convenience for setting up unique identifier columns
(similar to the <code class="literal">AUTO_INCREMENT</code> property
supported by some other databases). In the current
implementation, specifying
</p>
<pre class="programlisting">CREATE TABLE <em class="replaceable"><code>tablename</code></em> (
<em class="replaceable"><code>colname</code></em> SERIAL
);</pre>
<p>
is equivalent to specifying:
</p>
<pre class="programlisting">CREATE SEQUENCE <em class="replaceable"><code>tablename</code></em>_<em class="replaceable"><code>colname</code></em>_seq;
CREATE TABLE <em class="replaceable"><code>tablename</code></em> (
<em class="replaceable"><code>colname</code></em> integer DEFAULT nextval('<em class="replaceable"><code>tablename</code></em>_<em class="replaceable"><code>colname</code></em>_seq') NOT NULL
);</pre>
<p>
Thus, we have created an integer column and arranged for its default
values to be assigned from a sequence generator. A <code class="literal">NOT NULL</code>
constraint is applied to ensure that a null value cannot be explicitly
inserted, either. In most cases you would also want to attach a
<code class="literal">UNIQUE</code> or <code class="literal">PRIMARY KEY</code> constraint to prevent
duplicate values from being inserted by accident, but this is
not automatic.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
<p> Prior to <span class="productname">PostgreSQL</span> 7.3, <code class="type">serial</code>
implied <code class="literal">UNIQUE</code>. This is no longer automatic. If
you wish a serial column to be in a unique constraint or a
primary key, it must now be specified, same as with
any other data type.
</p>
</div>
<p> To insert the next value of the sequence into the <code class="type">serial</code>
column, specify that the <code class="type">serial</code>
column should be assigned its default value. This can be done
either by excluding the column from the list of columns in
the <code class="command">INSERT</code> statement, or through the use of
the <code class="literal">DEFAULT</code> key word.
</p>
<p> The type names <code class="type">serial</code> and <code class="type">serial4</code> are
equivalent: both create <code class="type">integer</code> columns. The type
names <code class="type">bigserial</code> and <code class="type">serial8</code> work just
the same way, except that they create a <code class="type">bigint</code>
column. <code class="type">bigserial</code> should be used if you anticipate
the use of more than 2<sup>31</sup> identifiers over the
lifetime of the table.
</p>
<p> The sequence created for a <code class="type">serial</code> column is
automatically dropped when the owning column is dropped, and
cannot be dropped otherwise. (This was not true in
<span class="productname">PostgreSQL</span> releases before 7.3. Note
that this automatic drop linkage will not occur for a sequence
created by reloading a dump from a pre-7.3 database; the dump
file does not contain the information needed to establish the
dependency link.) Furthermore, this dependency between sequence
and column is made only for the <code class="type">serial</code> column itself. If
any other columns reference the sequence (perhaps by manually
calling the <code class="function">nextval</code> function), they will be broken
if the sequence is removed. Using a <code class="type">serial</code> column's sequence
in such a fashion is considered bad form; if you wish to feed several
columns from the same sequence generator, create the sequence as an
independent object.
</p>
</div>
</div>
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