CREATE SEQUENCE(7) PostgreSQL 18.6 Documentation CREATE SEQUENCE(7) NAME CREATE_SEQUENCE - define a new sequence generator SYNOPSIS CREATE [ { TEMPORARY | TEMP } | UNLOGGED ] SEQUENCE [ IF NOT EXISTS ] name [ AS data_type ] [ INCREMENT [ BY ] increment ] [ MINVALUE minvalue | NO MINVALUE ] [ MAXVALUE maxvalue | NO MAXVALUE ] [ [ NO ] CYCLE ] [ START [ WITH ] start ] [ CACHE cache ] [ OWNED BY { table_name.column_name | NONE } ] DESCRIPTION CREATE SEQUENCE creates a new sequence number generator. This involves cre- ating and initializing a new special single-row table with the name name. The generator will be owned by the user issuing the command. 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. After a sequence is created, you use the functions nextval, currval, and setval to operate on the sequence. These functions are documented in Sec- tion 9.17. Although you cannot update a sequence directly, you can use a query like: SELECT * FROM name; to examine the parameters and current state of a sequence. In particular, the last_value 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 nextval calls.) PARAMETERS TEMPORARY or TEMP 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 tempo- rary sequence exists, unless they are referenced with schema-qualified names. UNLOGGED 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 ini- tial state after a crash or unclean shutdown. Unlogged sequences are also not replicated to standby servers. Unlike unlogged tables, unlogged sequences do not offer a significant performance advantage. This option is mainly intended for sequences as- sociated 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. IF NOT EXISTS 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. name The name (optionally schema-qualified) of the sequence to be created. data_type The optional clause AS data_type specifies the data type of the se- quence. Valid types are smallint, integer, and bigint. bigint is the default. The data type determines the default minimum and maximum val- ues of the sequence. increment The optional clause INCREMENT BY increment 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 se- quence. The default value is 1. minvalue NO MINVALUE The optional clause MINVALUE minvalue determines the minimum value a sequence can generate. If this clause is not supplied or NO MINVALUE is specified, then defaults will be used. The default for an ascending se- quence is 1. The default for a descending sequence is the minimum value of the data type. maxvalue NO MAXVALUE The optional clause MAXVALUE maxvalue determines the maximum value for the sequence. If this clause is not supplied or NO MAXVALUE is speci- fied, then default values will be used. The default for an ascending sequence is the maximum value of the data type. The default for a de- scending sequence is -1. CYCLE NO CYCLE The CYCLE option allows the sequence to wrap around when the maxvalue or minvalue has been reached by an ascending or descending sequence re- spectively. If the limit is reached, the next number generated will be the minvalue or maxvalue, respectively. If NO CYCLE is specified, any calls to nextval after the sequence has reached its maximum value will return an error. If neither CYCLE or NO CYCLE are specified, NO CYCLE is the default. start The optional clause START WITH start allows the sequence to begin any- where. The default starting value is minvalue for ascending sequences and maxvalue for descending ones. cache The optional clause CACHE cache 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. OWNED BY table_name.column_name OWNED BY NONE The OWNED BY option causes the sequence to be associated with a spe- cific table column, such that if that column (or its whole table) is dropped, the sequence will be automatically dropped as well. The speci- fied table must have the same owner and be in the same schema as the sequence. OWNED BY NONE, the default, specifies that there is no such association. NOTES Use DROP SEQUENCE to remove a sequence. Sequences are based on bigint arithmetic, so the range cannot exceed the range of an eight-byte integer (-9223372036854775808 to 9223372036854775807). Because nextval and setval calls are never rolled back, sequence objects cannot be used if "gapless" 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 se- quence objects, especially if many transactions need sequence numbers con- currently. Unexpected results might be obtained if a cache setting greater than one is used for a sequence object that will be used concurrently by multiple ses- sions. Each session will allocate and cache successive sequence values dur- ing one access to the sequence object and increase the sequence object's last_value accordingly. Then, the next cache-1 uses of nextval 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 "holes" in the sequence. 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 cache setting of 10, session A might reserve values 1..10 and return nextval=1, then session B might re- serve values 11..20 and return nextval=11 before session A has generated nextval=2. Thus, with a cache setting of one it is safe to assume that nextval values are generated sequentially; with a cache setting greater than one you should only assume that the nextval values are all distinct, not that they are generated purely sequentially. Also, last_value will re- flect the latest value reserved by any session, whether or not it has yet been returned by nextval. Another consideration is that a setval executed on such a sequence will not be noticed by other sessions until they have used up any preallocated val- ues they have cached. EXAMPLES Create an ascending sequence called serial, starting at 101: CREATE SEQUENCE serial START 101; Select the next number from this sequence: SELECT nextval('serial'); nextval --------- 101 Select the next number from this sequence: SELECT nextval('serial'); nextval --------- 102 Use this sequence in an INSERT command: INSERT INTO distributors VALUES (nextval('serial'), 'nothing'); Update the sequence value after a COPY FROM: BEGIN; COPY distributors FROM 'input_file'; SELECT setval('serial', max(id)) FROM distributors; END; COMPATIBILITY CREATE SEQUENCE conforms to the SQL standard, with the following excep- tions: * Obtaining the next value is done using the nextval() function instead of the standard's NEXT VALUE FOR expression. * The OWNED BY clause is a PostgreSQL extension. SEE ALSO ALTER SEQUENCE (ALTER_SEQUENCE(7)), DROP SEQUENCE (DROP_SEQUENCE(7)) PostgreSQL 18.6 2026 CREATE SEQUENCE(7)
NAME | SYNOPSIS | DESCRIPTION | PARAMETERS | NOTES | EXAMPLES | COMPATIBILITY | SEE ALSO
Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=CREATE_SEQUENCE&sektion=7&manpath=FreeBSD+Ports+15.1.quarterly>