1CREATE SEQUENCE(7) PostgreSQL 11.6 Documentation CREATE SEQUENCE(7)
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6 CREATE_SEQUENCE - define a new sequence generator
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9 CREATE [ TEMPORARY | TEMP ] SEQUENCE [ IF NOT EXISTS ] name
10 [ AS data_type ]
11 [ INCREMENT [ BY ] increment ]
12 [ MINVALUE minvalue | NO MINVALUE ] [ MAXVALUE maxvalue | NO MAXVALUE ]
13 [ START [ WITH ] start ] [ CACHE cache ] [ [ NO ] CYCLE ]
14 [ OWNED BY { table_name.column_name | NONE } ]
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17 CREATE SEQUENCE creates a new sequence number generator. This involves
18 creating and initializing a new special single-row table with the name
19 name. The generator will be owned by the user issuing the command.
20 If a schema name is given then the sequence is created in the specified
22 schema. Otherwise it is created in the current schema. Temporary
23 sequences exist in a special schema, so a schema name cannot be given
24 when creating a temporary sequence. The sequence name must be distinct
25 from the name of any other sequence, table, index, view, or foreign
26 table in the same schema.
27 After a sequence is created, you use the functions nextval, currval,
29 and setval to operate on the sequence. These functions are documented
30 in Section 9.16.
31 Although you cannot update a sequence directly, you can use a query
33 like:
34 SELECT * FROM name;
36 to examine the parameters and current state of a sequence. In
38 particular, the last_value field of the sequence shows the last value
39 allocated by any session. (Of course, this value might be obsolete by
40 the time it's printed, if other sessions are actively doing nextval
41 calls.)
42
44 TEMPORARY or TEMP
45 If specified, the sequence object is created only for this session,
46 and is automatically dropped on session exit. Existing permanent
47 sequences with the same name are not visible (in this session)
48 while the temporary sequence exists, unless they are referenced
49 with schema-qualified names.
50 IF NOT EXISTS
52 Do not throw an error if a relation with the same name already
53 exists. A notice is issued in this case. Note that there is no
54 guarantee that the existing relation is anything like the sequence
55 that would have been created - it might not even be a sequence.
56 name
58 The name (optionally schema-qualified) of the sequence to be
59 created.
60 data_type
62 The optional clause AS data_type specifies the data type of the
63 sequence. Valid types are smallint, integer, and bigint. bigint is
64 the default. The data type determines the default minimum and
65 maximum values of the sequence.
66 increment
68 The optional clause INCREMENT BY increment specifies which value is
69 added to the current sequence value to create a new value. A
70 positive value will make an ascending sequence, a negative one a
71 descending sequence. The default value is 1.
72 minvalue
74 NO MINVALUE
75 The optional clause MINVALUE minvalue determines the minimum value
76 a sequence can generate. If this clause is not supplied or NO
77 MINVALUE is specified, then defaults will be used. The default for
78 an ascending sequence is 1. The default for a descending sequence
79 is the minimum value of the data type.
80 maxvalue
82 NO MAXVALUE
83 The optional clause MAXVALUE maxvalue determines the maximum value
84 for the sequence. If this clause is not supplied or NO MAXVALUE is
85 specified, then default values will be used. The default for an
86 ascending sequence is the maximum value of the data type. The
87 default for a descending sequence is -1.
88 start
90 The optional clause START WITH start allows the sequence to begin
91 anywhere. The default starting value is minvalue for ascending
92 sequences and maxvalue for descending ones.
93 cache
95 The optional clause CACHE cache specifies how many sequence numbers
96 are to be preallocated and stored in memory for faster access. The
97 minimum value is 1 (only one value can be generated at a time,
98 i.e., no cache), and this is also the default.
99 CYCLE
101 NO CYCLE
102 The CYCLE option allows the sequence to wrap around when the
103 maxvalue or minvalue has been reached by an ascending or descending
104 sequence respectively. If the limit is reached, the next number
105 generated will be the minvalue or maxvalue, respectively.
106 If NO CYCLE is specified, any calls to nextval after the sequence
108 has reached its maximum value will return an error. If neither
109 CYCLE or NO CYCLE are specified, NO CYCLE is the default.
110 OWNED BY table_name.column_name
112 OWNED BY NONE
113 The OWNED BY option causes the sequence to be associated with a
114 specific table column, such that if that column (or its whole
115 table) is dropped, the sequence will be automatically dropped as
116 well. The specified table must have the same owner and be in the
117 same schema as the sequence. OWNED BY NONE, the default, specifies
118 that there is no such association.
119
121 Use DROP SEQUENCE to remove a sequence.
122 Sequences are based on bigint arithmetic, so the range cannot exceed
124 the range of an eight-byte integer (-9223372036854775808 to
125 9223372036854775807).
126 Because nextval and setval calls are never rolled back, sequence
128 objects cannot be used if “gapless” assignment of sequence numbers is
129 needed. It is possible to build gapless assignment by using exclusive
130 locking of a table containing a counter; but this solution is much more
131 expensive than sequence objects, especially if many transactions need
132 sequence numbers concurrently.
133 Unexpected results might be obtained if a cache setting greater than
135 one is used for a sequence object that will be used concurrently by
136 multiple sessions. Each session will allocate and cache successive
137 sequence values during one access to the sequence object and increase
138 the sequence object's last_value accordingly. Then, the next cache-1
139 uses of nextval within that session simply return the preallocated
140 values without touching the sequence object. So, any numbers allocated
141 but not used within a session will be lost when that session ends,
142 resulting in “holes” in the sequence.
143 Furthermore, although multiple sessions are guaranteed to allocate
145 distinct sequence values, the values might be generated out of sequence
146 when all the sessions are considered. For example, with a cache setting
147 of 10, session A might reserve values 1..10 and return nextval=1, then
148 session B might reserve values 11..20 and return nextval=11 before
149 session A has generated nextval=2. Thus, with a cache setting of one it
150 is safe to assume that nextval values are generated sequentially; with
151 a cache setting greater than one you should only assume that the
152 nextval values are all distinct, not that they are generated purely
153 sequentially. Also, last_value will reflect the latest value reserved
154 by any session, whether or not it has yet been returned by nextval.
155 Another consideration is that a setval executed on such a sequence will
157 not be noticed by other sessions until they have used up any
158 preallocated values they have cached.
159
161 Create an ascending sequence called serial, starting at 101:
162 CREATE SEQUENCE serial START 101;
164 Select the next number from this sequence:
166 SELECT nextval('serial');
168 nextval
170 ---------
171 101
172 Select the next number from this sequence:
174 SELECT nextval('serial');
176 nextval
178 ---------
179 102
180 Use this sequence in an INSERT command:
182 INSERT INTO distributors VALUES (nextval('serial'), 'nothing');
184 Update the sequence value after a COPY FROM:
186 BEGIN;
188 COPY distributors FROM 'input_file';
189 SELECT setval('serial', max(id)) FROM distributors;
190 END;
191
193 CREATE SEQUENCE conforms to the SQL standard, with the following
194 exceptions:
195 · Obtaining the next value is done using the nextval() function
197 instead of the standard's NEXT VALUE FOR expression.
198 · The OWNED BY clause is a PostgreSQL extension.
200
202 ALTER SEQUENCE (ALTER_SEQUENCE(7)), DROP SEQUENCE (DROP_SEQUENCE(7))
203PostgreSQL 11.6 2019 CREATE SEQUENCE(7)