1CREATE SEQUENCE() SQL Commands CREATE SEQUENCE()
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6 CREATE SEQUENCE - define a new sequence generator
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10 CREATE [ TEMPORARY | TEMP ] SEQUENCE name [ INCREMENT [ BY ] increment ]
11 [ MINVALUE minvalue | NO MINVALUE ] [ MAXVALUE maxvalue | NO MAXVALUE ]
12 [ START [ WITH ] start ] [ CACHE cache ] [ [ NO ] CYCLE ]
13 [ OWNED BY { table.column | 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 may not be given
24 when creating a temporary sequence. The sequence name must be distinct
25 from the name of any other sequence, table, index, or view in the same
26 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 in the documentation.
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 particu‐
38 lar, the last_value field of the sequence shows the last value allo‐
39 cated by any session. (Of course, this value may be obsolete by the
40 time it's printed, if other sessions are actively doing nextval calls.)
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43 TEMPORARY or TEMP
44 If specified, the sequence object is created only for this ses‐
45 sion, and is automatically dropped on session exit. Existing
46 permanent sequences with the same name are not visible (in this
47 session) while the temporary sequence exists, unless they are
48 referenced with schema-qualified names.
49 name The name (optionally schema-qualified) of the sequence to be
51 created.
52 increment
54 The optional clause INCREMENT BY increment specifies which value
55 is added to the current sequence value to create a new value. A
56 positive value will make an ascending sequence, a negative one a
57 descending sequence. The default value is 1.
58 minvalue
60 NO MINVALUE
62 The optional clause MINVALUE minvalue determines the minimum
63 value a sequence can generate. If this clause is not supplied or
64 NO MINVALUE is specified, then defaults will be used. The
65 defaults are 1 and -263-1 for ascending and descending
66 sequences, respectively.
67 maxvalue
69 NO MAXVALUE
71 The optional clause MAXVALUE maxvalue determines the maximum
72 value for the sequence. If this clause is not supplied or NO
73 MAXVALUE is specified, then default values will be used. The
74 defaults are 263-1 and -1 for ascending and descending
75 sequences, respectively.
76 start The optional clause START WITH start allows the sequence to
78 begin anywhere. The default starting value is minvalue for
79 ascending sequences and maxvalue for descending ones.
80 cache The optional clause CACHE cache specifies how many sequence num‐
82 bers are to be preallocated and stored in memory for faster
83 access. The minimum value is 1 (only one value can be generated
84 at a time, i.e., no cache), and this is also the default.
85 CYCLE
87 NO CYCLE
89 The CYCLE option allows the sequence to wrap around when the
90 maxvalue or minvalue has been reached by an ascending or
91 descending sequence respectively. If the limit is reached, the
92 next number generated will be the minvalue or maxvalue, respec‐
93 tively.
94 If NO CYCLE is specified, any calls to nextval after the
96 sequence has reached its maximum value will return an error. If
97 neither CYCLE or NO CYCLE are specified, NO CYCLE is the
98 default.
99 OWNED BY table.column
101 OWNED BY NONE
103 The OWNED BY option causes the sequence to be associated with a
104 specific table column, such that if that column (or its whole
105 table) is dropped, the sequence will be automatically dropped as
106 well. The specified table must have the same owner and be in the
107 same schema as the sequence. OWNED BY NONE, the default, speci‐
108 fies that there is no such association.
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111 Use DROP SEQUENCE to remove a sequence.
112 Sequences are based on bigint arithmetic, so the range cannot exceed
114 the range of an eight-byte integer (-9223372036854775808 to
115 9223372036854775807). On some older platforms, there may be no compiler
116 support for eight-byte integers, in which case sequences use regular
117 integer arithmetic (range -2147483648 to +2147483647).
118 Unexpected results may be obtained if a cache setting greater than one
120 is used for a sequence object that will be used concurrently by multi‐
121 ple sessions. Each session will allocate and cache successive sequence
122 values during one access to the sequence object and increase the
123 sequence object's last_value accordingly. Then, the next cache-1 uses
124 of nextval within that session simply return the preallocated values
125 without touching the sequence object. So, any numbers allocated but not
126 used within a session will be lost when that session ends, resulting in
127 ``holes'' in the sequence.
128 Furthermore, although multiple sessions are guaranteed to allocate dis‐
130 tinct sequence values, the values may be generated out of sequence when
131 all the sessions are considered. For example, with a cache setting of
132 10, session A might reserve values 1..10 and return nextval=1, then
133 session B might reserve values 11..20 and return nextval=11 before ses‐
134 sion A has generated nextval=2. Thus, with a cache setting of one it is
135 safe to assume that nextval values are generated sequentially; with a
136 cache setting greater than one you should only assume that the nextval
137 values are all distinct, not that they are generated purely sequen‐
138 tially. Also, last_value will reflect the latest value reserved by any
139 session, whether or not it has yet been returned by nextval.
140 Another consideration is that a setval executed on such a sequence will
142 not be noticed by other sessions until they have used up any preallo‐
143 cated values they have cached.
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146 Create an ascending sequence called serial, starting at 101:
147 CREATE SEQUENCE serial START 101;
149 Select the next number from this sequence:
152 SELECT nextval('serial');
154 nextval
156 ---------
157 114
158 Use this sequence in an INSERT command:
161 INSERT INTO distributors VALUES (nextval('serial'), 'nothing');
163 Update the sequence value after a COPY FROM:
166 BEGIN;
168 COPY distributors FROM 'input_file';
169 SELECT setval('serial', max(id)) FROM distributors;
170 END;
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174 CREATE SEQUENCE conforms to the SQL standard, with the following excep‐
175 tions:
176 · The standard's AS <data type> expression is not supported.
178 · Obtaining the next value is done using the nextval() function instead
180 of the standard's NEXT VALUE FOR expression.
181 · The OWNED BY clause is a PostgreSQL extension.
183
185 ALTER SEQUENCE [alter_sequence(7)], DROP SEQUENCE [drop_sequence(l)]
186SQL - Language Statements 2008-06-08 CREATE SEQUENCE()