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  1. <?xml version="1.0" encoding="UTF-8" standalone="no"?>

  2. <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>CREATE SEQUENCE</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><link rel="prev" href="sql-createschema.html" title="CREATE SCHEMA" /><link rel="next" href="sql-createserver.html" title="CREATE SERVER" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">CREATE SEQUENCE</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="sql-createschema.html" title="CREATE SCHEMA">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="sql-commands.html" title="SQL Commands">Up</a></td><th width="60%" align="center">SQL Commands</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="sql-createserver.html" title="CREATE SERVER">Next</a></td></tr></table><hr></hr></div><div class="refentry" id="SQL-CREATESEQUENCE"><div class="titlepage"></div><a id="id-1.9.3.81.1" class="indexterm"></a><div class="refnamediv"><h2><span class="refentrytitle">CREATE SEQUENCE</span></h2><p>CREATE SEQUENCE — define a new sequence generator</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><pre class="synopsis">

  3. CREATE [ TEMPORARY | TEMP ] SEQUENCE [ IF NOT EXISTS ] <em class="replaceable"><code>name</code></em>

  4.     [ AS <em class="replaceable"><code>data_type</code></em> ]

  5.     [ INCREMENT [ BY ] <em class="replaceable"><code>increment</code></em> ]

  6.     [ MINVALUE <em class="replaceable"><code>minvalue</code></em> | NO MINVALUE ] [ MAXVALUE <em class="replaceable"><code>maxvalue</code></em> | NO MAXVALUE ]

  7.     [ START [ WITH ] <em class="replaceable"><code>start</code></em> ] [ CACHE <em class="replaceable"><code>cache</code></em> ] [ [ NO ] CYCLE ]

  8.     [ OWNED BY { <em class="replaceable"><code>table_name</code></em>.<em class="replaceable"><code>column_name</code></em> | NONE } ]

  9. </pre></div><div class="refsect1" id="id-1.9.3.81.5"><h2>Description</h2><p>

  10.    <code class="command">CREATE SEQUENCE</code> creates a new sequence number

  11.    generator.  This involves creating and initializing a new special

  12.    single-row table with the name <em class="replaceable"><code>name</code></em>.  The generator will be

  13.    owned by the user issuing the command.

  14.   </p><p>

  15.    If a schema name is given then the sequence is created in the

  16.    specified schema.  Otherwise it is created in the current schema.

  17.    Temporary sequences exist in a special schema, so a schema name cannot be

  18.    given when creating a temporary sequence.

  19.    The sequence name must be distinct from the name of any other sequence,

  20.    table, index, view, or foreign table in the same schema.

  21.   </p><p>

  22.    After a sequence is created, you use the functions

  23.    <code class="function">nextval</code>,

  24.    <code class="function">currval</code>, and

  25.    <code class="function">setval</code>

  26.    to operate on the sequence.  These functions are documented in

  27.    <a class="xref" href="functions-sequence.html" title="9.16. Sequence Manipulation Functions">Section 9.16</a>.

  28.   </p><p>

  29.    Although you cannot update a sequence directly, you can use a query like:

  30. 

  31. </p><pre class="programlisting">

  32. SELECT * FROM <em class="replaceable"><code>name</code></em>;

  33. </pre><p>

  34. 

  35.    to examine the parameters and current state of a sequence.  In particular,

  36.    the <code class="literal">last_value</code> field of the sequence shows the last value

  37.    allocated by any session.  (Of course, this value might be obsolete

  38.    by the time it's printed, if other sessions are actively doing

  39.    <code class="function">nextval</code> calls.)

  40.   </p></div><div class="refsect1" id="id-1.9.3.81.6"><h2>Parameters</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="literal">TEMPORARY</code> or <code class="literal">TEMP</code></span></dt><dd><p>

  41.       If specified, the sequence object is created only for this

  42.       session, and is automatically dropped on session exit.  Existing

  43.       permanent sequences with the same name are not visible (in this

  44.       session) while the temporary sequence exists, unless they are

  45.       referenced with schema-qualified names.

  46.      </p></dd><dt><span class="term"><code class="literal">IF NOT EXISTS</code></span></dt><dd><p>

  47.       Do not throw an error if a relation with the same name already exists.

  48.       A notice is issued in this case. Note that there is no guarantee that

  49.       the existing relation is anything like the sequence that would have

  50.       been created - it might not even be a sequence.

  51.      </p></dd><dt><span class="term"><em class="replaceable"><code>name</code></em></span></dt><dd><p>

  52.       The name (optionally schema-qualified) of the sequence to be created.

  53.      </p></dd><dt><span class="term"><em class="replaceable"><code>data_type</code></em></span></dt><dd><p>

  54.       The optional

  55.       clause <code class="literal">AS <em class="replaceable"><code>data_type</code></em></code>

  56.       specifies the data type of the sequence.  Valid types are

  57.       <code class="literal">smallint</code>, <code class="literal">integer</code>,

  58.       and <code class="literal">bigint</code>.  <code class="literal">bigint</code> is the

  59.       default.  The data type determines the default minimum and maximum

  60.       values of the sequence.

  61.      </p></dd><dt><span class="term"><em class="replaceable"><code>increment</code></em></span></dt><dd><p>

  62.       The optional clause <code class="literal">INCREMENT BY <em class="replaceable"><code>increment</code></em></code> specifies

  63.       which value is added to the current sequence value to create a

  64.       new value.  A positive value will make an ascending sequence, a

  65.       negative one a descending sequence.  The default value is 1.

  66.      </p></dd><dt><span class="term"><em class="replaceable"><code>minvalue</code></em><br /></span><span class="term"><code class="literal">NO MINVALUE</code></span></dt><dd><p>

  67.       The optional clause <code class="literal">MINVALUE <em class="replaceable"><code>minvalue</code></em></code> determines

  68.       the minimum value a sequence can generate. If this clause is not

  69.       supplied or <code class="option">NO MINVALUE</code> is specified, then

  70.       defaults will be used.  The default for an ascending sequence is 1.  The

  71.       default for a descending sequence is the minimum value of the data type.

  72.      </p></dd><dt><span class="term"><em class="replaceable"><code>maxvalue</code></em><br /></span><span class="term"><code class="literal">NO MAXVALUE</code></span></dt><dd><p>

  73.       The optional clause <code class="literal">MAXVALUE <em class="replaceable"><code>maxvalue</code></em></code> determines

  74.       the maximum value for the sequence. If this clause is not

  75.       supplied or <code class="option">NO MAXVALUE</code> is specified, then

  76.       default values will be used.  The default for an ascending sequence is

  77.       the maximum value of the data type.  The default for a descending

  78.       sequence is -1.

  79.      </p></dd><dt><span class="term"><em class="replaceable"><code>start</code></em></span></dt><dd><p>

  80.       The optional clause <code class="literal">START WITH <em class="replaceable"><code>start</code></em> </code> allows the

  81.       sequence to begin anywhere.  The default starting value is

  82.       <em class="replaceable"><code>minvalue</code></em> for

  83.       ascending sequences and <em class="replaceable"><code>maxvalue</code></em> for descending ones.

  84.      </p></dd><dt><span class="term"><em class="replaceable"><code>cache</code></em></span></dt><dd><p>

  85.       The optional clause <code class="literal">CACHE <em class="replaceable"><code>cache</code></em></code> specifies how

  86.       many sequence numbers are to be preallocated and stored in

  87.       memory for faster access. The minimum value is 1 (only one value

  88.       can be generated at a time, i.e., no cache), and this is also the

  89.       default.

  90.      </p></dd><dt><span class="term"><code class="literal">CYCLE</code><br /></span><span class="term"><code class="literal">NO CYCLE</code></span></dt><dd><p>

  91.       The <code class="literal">CYCLE</code> option allows the sequence to wrap

  92.       around when the <em class="replaceable"><code>maxvalue</code></em> or <em class="replaceable"><code>minvalue</code></em> has been reached by an

  93.       ascending or descending sequence respectively. If the limit is

  94.       reached, the next number generated will be the <em class="replaceable"><code>minvalue</code></em> or <em class="replaceable"><code>maxvalue</code></em>, respectively.

  95.      </p><p>

  96.       If <code class="literal">NO CYCLE</code> is specified, any calls to

  97.       <code class="function">nextval</code> after the sequence has reached its

  98.       maximum value will return an error.  If neither

  99.       <code class="literal">CYCLE</code> or <code class="literal">NO CYCLE</code> are

  100.       specified, <code class="literal">NO CYCLE</code> is the default.

  101.      </p></dd><dt><span class="term"><code class="literal">OWNED BY</code> <em class="replaceable"><code>table_name</code></em>.<em class="replaceable"><code>column_name</code></em><br /></span><span class="term"><code class="literal">OWNED BY NONE</code></span></dt><dd><p>

  102.       The <code class="literal">OWNED BY</code> option causes the sequence to be

  103.       associated with a specific table column, such that if that column

  104.       (or its whole table) is dropped, the sequence will be automatically

  105.       dropped as well.  The specified table must have the same owner and be in

  106.       the same schema as the sequence.

  107.       <code class="literal">OWNED BY NONE</code>, the default, specifies that there

  108.       is no such association.

  109.      </p></dd></dl></div></div><div class="refsect1" id="id-1.9.3.81.7"><h2>Notes</h2><p>

  110.    Use <code class="command">DROP SEQUENCE</code> to remove a sequence.

  111.   </p><p>

  112.    Sequences are based on <code class="type">bigint</code> arithmetic, so the range

  113.    cannot exceed the range of an eight-byte integer

  114.    (-9223372036854775808 to 9223372036854775807).

  115.   </p><p>

  116.    Because <code class="function">nextval</code> and <code class="function">setval</code> calls are never

  117.    rolled back, sequence objects cannot be used if <span class="quote">“<span class="quote">gapless</span>”</span>

  118.    assignment of sequence numbers is needed.  It is possible to build

  119.    gapless assignment by using exclusive locking of a table containing a

  120.    counter; but this solution is much more expensive than sequence

  121.    objects, especially if many transactions need sequence numbers

  122.    concurrently.

  123.   </p><p>

  124.    Unexpected results might be obtained if a <em class="replaceable"><code>cache</code></em> setting greater than one is

  125.    used for a sequence object that will be used concurrently by

  126.    multiple sessions.  Each session will allocate and cache successive

  127.    sequence values during one access to the sequence object and

  128.    increase the sequence object's <code class="literal">last_value</code> accordingly.

  129.    Then, the next <em class="replaceable"><code>cache</code></em>-1

  130.    uses of <code class="function">nextval</code> within that session simply return the

  131.    preallocated values without touching the sequence object.  So, any

  132.    numbers allocated but not used within a session will be lost when

  133.    that session ends, resulting in <span class="quote">“<span class="quote">holes</span>”</span> in the

  134.    sequence.

  135.   </p><p>

  136.    Furthermore, although multiple sessions are guaranteed to allocate

  137.    distinct sequence values, the values might be generated out of

  138.    sequence when all the sessions are considered.  For example, with

  139.    a <em class="replaceable"><code>cache</code></em> setting of 10,

  140.    session A might reserve values 1..10 and return

  141.    <code class="function">nextval</code>=1, then session B might reserve values

  142.    11..20 and return <code class="function">nextval</code>=11 before session A

  143.    has generated <code class="literal">nextval</code>=2.  Thus, with a

  144.    <em class="replaceable"><code>cache</code></em> setting of one

  145.    it is safe to assume that <code class="function">nextval</code> values are generated

  146.    sequentially; with a <em class="replaceable"><code>cache</code></em> setting greater than one you

  147.    should only assume that the <code class="function">nextval</code> values are all

  148.    distinct, not that they are generated purely sequentially.  Also,

  149.    <code class="literal">last_value</code> will reflect the latest value reserved by

  150.    any session, whether or not it has yet been returned by

  151.    <code class="function">nextval</code>.

  152.   </p><p>

  153.    Another consideration is that a <code class="function">setval</code> executed on

  154.    such a sequence will not be noticed by other sessions until they

  155.    have used up any preallocated values they have cached.

  156.   </p></div><div class="refsect1" id="id-1.9.3.81.8"><h2>Examples</h2><p>

  157.    Create an ascending sequence called <code class="literal">serial</code>, starting at 101:

  158. </p><pre class="programlisting">

  159. CREATE SEQUENCE serial START 101;

  160. </pre><p>

  161.   </p><p>

  162.    Select the next number from this sequence:

  163. </p><pre class="programlisting">

  164. SELECT nextval('serial');

  165. 

  166.  nextval

  167. ---------

  168.      101

  169. </pre><p>

  170.   </p><p>

  171.    Select the next number from this sequence:

  172. </p><pre class="programlisting">

  173. SELECT nextval('serial');

  174. 

  175.  nextval

  176. ---------

  177.      102

  178. </pre><p>

  179.   </p><p>

  180.    Use this sequence in an <code class="command">INSERT</code> command:

  181. </p><pre class="programlisting">

  182. INSERT INTO distributors VALUES (nextval('serial'), 'nothing');

  183. </pre><p>

  184.   </p><p>

  185.    Update the sequence value after a <code class="command">COPY FROM</code>:

  186. </p><pre class="programlisting">

  187. BEGIN;

  188. COPY distributors FROM 'input_file';

  189. SELECT setval('serial', max(id)) FROM distributors;

  190. END;

  191. </pre></div><div class="refsect1" id="id-1.9.3.81.9"><h2>Compatibility</h2><p>

  192.    <code class="command">CREATE SEQUENCE</code> conforms to the <acronym class="acronym">SQL</acronym>

  193.    standard, with the following exceptions:

  194.    </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>

  195.       Obtaining the next value is done using the <code class="function">nextval()</code>

  196.       function instead of the standard's <code class="command">NEXT VALUE FOR</code>

  197.       expression.

  198.      </p></li><li class="listitem"><p>

  199.       The <code class="literal">OWNED BY</code> clause is a <span class="productname">PostgreSQL</span>

  200.       extension.

  201.      </p></li></ul></div></div><div class="refsect1" id="id-1.9.3.81.10"><h2>See Also</h2><span class="simplelist"><a class="xref" href="sql-altersequence.html" title="ALTER SEQUENCE"><span class="refentrytitle">ALTER SEQUENCE</span></a>, <a class="xref" href="sql-dropsequence.html" title="DROP SEQUENCE"><span class="refentrytitle">DROP SEQUENCE</span></a></span></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="sql-createschema.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="sql-commands.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="sql-createserver.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">CREATE SCHEMA </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> CREATE SERVER</td></tr></table></div></body></html>
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