1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
|
<?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 id="docContent" class="container-fluid col-10"><div 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 16.2 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 /></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 } | UNLOGGED ] 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 relation
(table, sequence, index, view, materialized 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="9.17. Sequence Manipulation Functions">Section 9.17</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">UNLOGGED</code></span></dt><dd><p>
If specified, the sequence is created as an unlogged sequence. Changes
to unlogged sequences are not written to the write-ahead log. They are
not crash-safe: an unlogged sequence is automatically reset to its
initial state after a crash or unclean shutdown. Unlogged sequences are
also not replicated to standby servers.
</p><p>
Unlike unlogged tables, unlogged sequences do not offer a significant
performance advantage. This option is mainly intended for sequences
associated with unlogged tables via identity columns or serial columns.
In those cases, it usually wouldn't make sense to have the sequence
WAL-logged and replicated but not its associated table.
</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="function">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" title="CREATE SCHEMA">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="sql-commands.html" title="SQL Commands">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="sql-createserver.html" title="CREATE SERVER">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" title="PostgreSQL 16.2 Documentation">Home</a></td><td width="40%" align="right" valign="top"> CREATE SERVER</td></tr></table></div></body></html>
|
