The CREATE SEQUENCE statement creates a new sequence number generator.
Examples
Generate an ascending sequence starting from 1:
CREATE SEQUENCE serial;
Generate sequence from a given start number:
CREATE SEQUENCE serial START 101;
Generate odd numbers using INCREMENT BY:
CREATE SEQUENCE serial START WITH 1 INCREMENT BY 2;
Generate a descending sequence starting from 99:
CREATE SEQUENCE serial START WITH 99 INCREMENT BY -1 MAXVALUE 99;
By default, cycles are not allowed and will result in error, e.g.:
Sequence Error: nextval: reached maximum value of sequence "serial" (10)
CREATE SEQUENCE serial START WITH 1 MAXVALUE 10;
CYCLE allows cycling through the same sequence repeatedly:
CREATE SEQUENCE serial START WITH 1 MAXVALUE 10 CYCLE;
Creating and Dropping Sequences
Sequences can be created and dropped similarly to other catalogue items.
Overwrite an existing sequence:
CREATE OR REPLACE SEQUENCE serial;
Only create sequence if no such sequence exists yet:
CREATE SEQUENCE IF NOT EXISTS serial;
Remove sequence:
DROP SEQUENCE serial;
Remove sequence if exists:
DROP SEQUENCE IF EXISTS serial;
Using Sequences for Primary Keys
Sequences can provide an integer primary key for a table. For example:
CREATE SEQUENCE id_sequence START 1;
CREATE TABLE tbl (id INTEGER DEFAULT nextval('id_sequence'), s VARCHAR);
INSERT INTO tbl (s) VALUES ('hello'), ('world');
SELECT * FROM tbl;
The script results in the following table:
| id | s |
|---|---|
| 1 | hello |
| 2 | world |
Sequences can also be added using the ALTER TABLE statement. The following example adds an id column and fills it with values generated by the sequence:
CREATE TABLE tbl (s VARCHAR);
INSERT INTO tbl VALUES ('hello'), ('world');
CREATE SEQUENCE id_sequence START 1;
ALTER TABLE tbl ADD COLUMN id INTEGER DEFAULT nextval('id_sequence');
SELECT * FROM tbl;
This script results in the same table as the previous example.
Selecting the Next Value
To select the next number from a sequence, use nextval:
CREATE SEQUENCE serial START 1;
SELECT nextval('serial') AS nextval;
| nextval |
|---|
| 1 |
Using this sequence in an INSERT command:
INSERT INTO distributors VALUES (nextval('serial'), 'nothing');
Selecting the Current Value
You may also view the current number from the sequence. Note that the nextval function must have already been called before calling currval, otherwise a Serialization Error (sequence is not yet defined in this session) will be thrown.
CREATE SEQUENCE serial START 1;
SELECT nextval('serial') AS nextval;
SELECT currval('serial') AS currval;
| currval |
|---|
| 1 |
Syntax
CREATE SEQUENCE creates a new sequence number generator.
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 may not be given when creating a temporary sequence. The sequence name must be distinct from the name of any other sequence in the same schema.
After a sequence is created, you use the function nextval to operate on the sequence.
Parameters
| Name | Description |
|---|---|
CYCLE or 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 respectively. 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. |
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 sequence. The default value is 1. |
maxvalue |
The optional clause MAXVALUE maxvalue determines the maximum value for the sequence. If this clause is not supplied or NO MAXVALUE is specified, then default values will be used. The defaults are 2^63 - 1 and -1 for ascending and descending sequences, respectively. |
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 defaults are 1 and -(2^63 - 1) for ascending and descending sequences, respectively. |
name |
The name (optionally schema-qualified) of the sequence to be created. |
start |
The optional clause START WITH start allows the sequence to begin anywhere. The default starting value is minvalue for ascending sequences and maxvalue for descending ones. |
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 temporary sequence exists, unless they are referenced with schema-qualified names. |
Sequences are based on
BIGINTarithmetic, so the range cannot exceed the range of an eight-byte integer (-9223372036854775808 to 9223372036854775807).