<?xml version="1.0" encoding="UTF-8" standalone="no"?> <!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 Vsnapshot" /><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 11.7 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"> CREATE [ TEMPORARY | TEMP ] SEQUENCE [ IF NOT EXISTS ] <em class="replaceable"><code>name</code></em> [ AS <em class="replaceable"><code>data_type</code></em> ] [ INCREMENT [ BY ] <em class="replaceable"><code>increment</code></em> ] [ MINVALUE <em class="replaceable"><code>minvalue</code></em> | NO MINVALUE ] [ MAXVALUE <em class="replaceable"><code>maxvalue</code></em> | NO MAXVALUE ] [ START [ WITH ] <em class="replaceable"><code>start</code></em> ] [ CACHE <em class="replaceable"><code>cache</code></em> ] [ [ NO ] CYCLE ] [ OWNED BY { <em class="replaceable"><code>table_name</code></em>.<em class="replaceable"><code>column_name</code></em> | NONE } ] </pre></div><div class="refsect1" id="id-1.9.3.81.5"><h2>Description</h2><p> <code class="command">CREATE SEQUENCE</code> creates a new sequence number generator. This involves creating and initializing a new special single-row table with the name <em class="replaceable"><code>name</code></em>. The generator will be owned by the user issuing the command. </p><p> If a schema name is given then the sequence is created in the specified schema. Otherwise it is created in the current schema. Temporary sequences exist in a special schema, so a schema name cannot be given when creating a temporary sequence. The sequence name must be distinct from the name of any other sequence, table, index, view, or foreign table in the same schema. </p><p> After a sequence is created, you use the functions <code class="function">nextval</code>, <code class="function">currval</code>, and <code class="function">setval</code> to operate on the sequence. These functions are documented in <a class="xref" href="functions-sequence.html" title="9.16. Sequence Manipulation Functions">Section 9.16</a>. </p><p> Although you cannot update a sequence directly, you can use a query like: </p><pre class="programlisting"> SELECT * FROM <em class="replaceable"><code>name</code></em>; </pre><p> to examine the parameters and current state of a sequence. In particular, the <code class="literal">last_value</code> field of the sequence shows the last value allocated by any session. (Of course, this value might be obsolete by the time it's printed, if other sessions are actively doing <code class="function">nextval</code> calls.) </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> If specified, the sequence object is created only for this session, and is automatically dropped on session exit. Existing permanent sequences with the same name are not visible (in this session) while the temporary sequence exists, unless they are referenced with schema-qualified names. </p></dd><dt><span class="term"><code class="literal">IF NOT EXISTS</code></span></dt><dd><p> Do not throw an error if a relation with the same name already exists. A notice is issued in this case. Note that there is no guarantee that the existing relation is anything like the sequence that would have been created - it might not even be a sequence. </p></dd><dt><span class="term"><em class="replaceable"><code>name</code></em></span></dt><dd><p> The name (optionally schema-qualified) of the sequence to be created. </p></dd><dt><span class="term"><em class="replaceable"><code>data_type</code></em></span></dt><dd><p> The optional clause <code class="literal">AS <em class="replaceable"><code>data_type</code></em></code> specifies the data type of the sequence. Valid types are <code class="literal">smallint</code>, <code class="literal">integer</code>, and <code class="literal">bigint</code>. <code class="literal">bigint</code> is the default. The data type determines the default minimum and maximum values of the sequence. </p></dd><dt><span class="term"><em class="replaceable"><code>increment</code></em></span></dt><dd><p> The optional clause <code class="literal">INCREMENT BY <em class="replaceable"><code>increment</code></em></code> specifies which value is added to the current sequence value to create a new value. A positive value will make an ascending sequence, a negative one a descending sequence. The default value is 1. </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> The optional clause <code class="literal">MINVALUE <em class="replaceable"><code>minvalue</code></em></code> determines the minimum value a sequence can generate. If this clause is not supplied or <code class="option">NO MINVALUE</code> is specified, then defaults will be used. The default for an ascending sequence is 1. The default for a descending sequence is the minimum value of the data type. </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> The optional clause <code class="literal">MAXVALUE <em class="replaceable"><code>maxvalue</code></em></code> determines the maximum value for the sequence. If this clause is not supplied or <code class="option">NO MAXVALUE</code> is specified, then default values will be used. The default for an ascending sequence is the maximum value of the data type. The default for a descending sequence is -1. </p></dd><dt><span class="term"><em class="replaceable"><code>start</code></em></span></dt><dd><p> The optional clause <code class="literal">START WITH <em class="replaceable"><code>start</code></em> </code> allows the sequence to begin anywhere. The default starting value is <em class="replaceable"><code>minvalue</code></em> for ascending sequences and <em class="replaceable"><code>maxvalue</code></em> for descending ones. </p></dd><dt><span class="term"><em class="replaceable"><code>cache</code></em></span></dt><dd><p> The optional clause <code class="literal">CACHE <em class="replaceable"><code>cache</code></em></code> specifies how many sequence numbers are to be preallocated and stored in memory for faster access. The minimum value is 1 (only one value can be generated at a time, i.e., no cache), and this is also the default. </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> The <code class="literal">CYCLE</code> option allows the sequence to wrap around when the <em class="replaceable"><code>maxvalue</code></em> or <em class="replaceable"><code>minvalue</code></em> has been reached by an ascending or descending sequence respectively. If the limit is reached, the next number generated will be the <em class="replaceable"><code>minvalue</code></em> or <em class="replaceable"><code>maxvalue</code></em>, respectively. </p><p> If <code class="literal">NO CYCLE</code> is specified, any calls to <code class="function">nextval</code> after the sequence has reached its maximum value will return an error. If neither <code class="literal">CYCLE</code> or <code class="literal">NO CYCLE</code> are specified, <code class="literal">NO CYCLE</code> is the default. </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> The <code class="literal">OWNED BY</code> option causes the sequence to be associated with a specific table column, such that if that column (or its whole table) is dropped, the sequence will be automatically dropped as well. The specified table must have the same owner and be in the same schema as the sequence. <code class="literal">OWNED BY NONE</code>, the default, specifies that there is no such association. </p></dd></dl></div></div><div class="refsect1" id="id-1.9.3.81.7"><h2>Notes</h2><p> Use <code class="command">DROP SEQUENCE</code> to remove a sequence. </p><p> Sequences are based on <code class="type">bigint</code> arithmetic, so the range cannot exceed the range of an eight-byte integer (-9223372036854775808 to 9223372036854775807). </p><p> Because <code class="function">nextval</code> and <code class="function">setval</code> calls are never rolled back, sequence objects cannot be used if <span class="quote">“<span class="quote">gapless</span>”</span> assignment of sequence numbers is needed. It is possible to build gapless assignment by using exclusive locking of a table containing a counter; but this solution is much more expensive than sequence objects, especially if many transactions need sequence numbers concurrently. </p><p> Unexpected results might be obtained if a <em class="replaceable"><code>cache</code></em> setting greater than one is used for a sequence object that will be used concurrently by multiple sessions. Each session will allocate and cache successive sequence values during one access to the sequence object and increase the sequence object's <code class="literal">last_value</code> accordingly. Then, the next <em class="replaceable"><code>cache</code></em>-1 uses of <code class="function">nextval</code> within that session simply return the preallocated values without touching the sequence object. So, any numbers allocated but not used within a session will be lost when that session ends, resulting in <span class="quote">“<span class="quote">holes</span>”</span> in the sequence. </p><p> Furthermore, although multiple sessions are guaranteed to allocate distinct sequence values, the values might be generated out of sequence when all the sessions are considered. For example, with a <em class="replaceable"><code>cache</code></em> setting of 10, session A might reserve values 1..10 and return <code class="function">nextval</code>=1, then session B might reserve values 11..20 and return <code class="function">nextval</code>=11 before session A has generated <code class="literal">nextval</code>=2. Thus, with a <em class="replaceable"><code>cache</code></em> setting of one it is safe to assume that <code class="function">nextval</code> values are generated sequentially; with a <em class="replaceable"><code>cache</code></em> setting greater than one you should only assume that the <code class="function">nextval</code> values are all distinct, not that they are generated purely sequentially. Also, <code class="literal">last_value</code> will reflect the latest value reserved by any session, whether or not it has yet been returned by <code class="function">nextval</code>. </p><p> Another consideration is that a <code class="function">setval</code> executed on such a sequence will not be noticed by other sessions until they have used up any preallocated values they have cached. </p></div><div class="refsect1" id="id-1.9.3.81.8"><h2>Examples</h2><p> Create an ascending sequence called <code class="literal">serial</code>, starting at 101: </p><pre class="programlisting"> CREATE SEQUENCE serial START 101; </pre><p> </p><p> Select the next number from this sequence: </p><pre class="programlisting"> SELECT nextval('serial'); nextval --------- 101 </pre><p> </p><p> Select the next number from this sequence: </p><pre class="programlisting"> SELECT nextval('serial'); nextval --------- 102 </pre><p> </p><p> Use this sequence in an <code class="command">INSERT</code> command: </p><pre class="programlisting"> INSERT INTO distributors VALUES (nextval('serial'), 'nothing'); </pre><p> </p><p> Update the sequence value after a <code class="command">COPY FROM</code>: </p><pre class="programlisting"> BEGIN; COPY distributors FROM 'input_file'; SELECT setval('serial', max(id)) FROM distributors; END; </pre></div><div class="refsect1" id="id-1.9.3.81.9"><h2>Compatibility</h2><p> <code class="command">CREATE SEQUENCE</code> conforms to the <acronym class="acronym">SQL</acronym> standard, with the following exceptions: </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p> Obtaining the next value is done using the <code class="function">nextval()</code> function instead of the standard's <code class="command">NEXT VALUE FOR</code> expression. </p></li><li class="listitem"><p> The <code class="literal">OWNED BY</code> clause is a <span class="productname">PostgreSQL</span> extension. </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>