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  6. CREATE SEQUENCE

CREATE SEQUENCE

Function

Sequence is a special table that stores arithmetic columns. Such a table is controlled by DBMS. It has no actual meaning and is usually used to generate unique identifiers for rows or tables.

CREATE SEQUENCE is used to add a new sequence to the current database. The owner of a sequence is the user who creates the sequence.

Precautions

If a schema name is given, the sequence is created in the specified schema; otherwise, it is created in the current schema. The sequence name must be different from the names of other sequences, tables, indexes, views in the same schema.

After the sequence is created, functions nextval() and generate_series(1,N) insert data to the table. Make sure that the number of times for invoking nextval is greater than or equal to N+1. Otherwise, errors will be reported because the number of times for invoking function generate_series() is N+1.

Syntax

CREATE SEQUENCE name [ INCREMENT [ BY ] increment ]
    [ MINVALUE minvalue | NO MINVALUE | NOMINVALUE ] [ MAXVALUE maxvalue | NO MAXVALUE | NOMAXVALUE] 
    [ START [ WITH ] start ] [ CACHE cache ] [ [ NO ] CYCLE | NOCYCLE ] 
    [ OWNED BY { table_name.column_name | NONE } ];

Parameter Description

  • name

    Indicates the name of the sequence to be created.

  • increment

    Specifies the step for a sequence. A positive generates an ascending sequence, and a negative generates a decreasing sequence.

    The default value is 1.

  • MINVALUE minvalue | NO MINVALUE| NOMINVALUE

    Specifies the minimum value of the sequence. If MINVALUE is not declared, or NO MINVALUE is declared, the default value of the ascending sequence is 1, and that of the descending sequence is -263-1. NOMINVALUE is equivalent to NO MINVALUE.

  • MAXVALUE maxvalue | NO MAXVALUE| NOMAXVALUE

    Specifies the maximum value in a sequence. If MAXVALUE is not declared or NO MINVALUE is declared, the default value of the ascending sequence is 263-1, and that of the descending sequence is -1. NOMAXVALUE is equivalent to NO MAXVALUE.

  • start

    Specifies the start value of the sequence. The default value for ascending sequences is minvalue and for descending sequences maxvalue.

  • cache

    Specifies the number sequences stored in the memory for quick access purposes.

    Default value 1 indicates that one value can be generated each time.

    NOTE:

    It is not recommended that you define cache, and maxvalue, and minvalue at the same time. The continuity of sequences cannot be ensured after cache is defined because valid characters may be generated, causing waste of sequences.

  • CYCLE

    Used to ensure that sequences can recycle after the number of sequences reaches maxvalue or minvalue.

    If you declare NO CYCLE, any invocation of nextval would return an error after the sequence reaches its maximum value.

    NOCYCLE is equivalent to NO CYCLE.

    The default value is NO CYCLE.

    If the sequence is defined as CYCLE, the sequence uniqueness cannot be ensured.

  • OWNED BY

    Associates a sequence with a specified column included in a table. In this way, the sequence will be deleted when you delete its associated field or the table where the field belongs. The associated table and sequence must be owned by the same user and in the same schema. OWNED BY only establishes the association between a table column and the sequence. The sequence is not created for this column.

    If the default value is OWNED BY NONE, indicating that such association does not exist.

    The specified table must be created on the default Node Group.

Examples

Create an ascending sequence named serial, which starts from 101:

CREATE SEQUENCE serial
 START 101
 CACHE 20;

Select the next number from the sequence:

SELECT nextval('serial');
 nextval 
 ---------
      101

Select the next number from the sequence:

SELECT nextval('serial');
 nextval 
 ---------
      102

Create a sequence associated with the table:

CREATE TABLE customer_address
(
    ca_address_sk             integer               not null,
    ca_address_id             char(16)              not null,
    ca_street_number          char(10)                      ,
    ca_street_name            varchar(60)                   ,
    ca_street_type            char(15)                      ,
    ca_suite_number           char(10)                      ,
    ca_city                   varchar(60)                   ,
    ca_county                 varchar(30)                   ,
    ca_state                  char(2)                       ,
    ca_zip                    char(10)                      ,
    ca_country                varchar(20)                   ,
    ca_gmt_offset             decimal(5,2)                  ,
    ca_location_type          char(20)                     
) ;

CREATE SEQUENCE serial1
 START 101
 CACHE 20
OWNED BY customer_address.ca_address_sk;
-- Delete the sequence.
DROP TABLE customer_address;
DROP SEQUENCE serial cascade;
DROP SEQUENCE serial1 cascade;