CREATE SEQUENCE

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The CREATE SEQUENCE statement creates a new sequence in a database. Use a sequence to auto-increment integers in a table.

Considerations

• Using a sequence is slower than auto-generating unique IDs with the gen_random_uuid(), uuid_v4() or unique_rowid() built-in functions. Incrementing a sequence requires a write to persistent storage, whereas auto-generating a unique ID does not. Therefore, use auto-generated unique IDs unless an incremental sequence is preferred or required.
• A column that uses a sequence can have a gap in the sequence values if a transaction advances the sequence and is then rolled back. Sequence updates are committed immediately and aren't rolled back along with their containing transaction. This is done to avoid blocking concurrent transactions that use the same sequence.

• For performance reasons, we discourage indexing on sequential keys. If, however, you are working with a table that must be indexed on sequential keys, you should use hash-sharded indexes. Hash-sharded indexes distribute sequential traffic uniformly across ranges, eliminating single-range hotspots and improving write performance on sequentially-keyed indexes at a small cost to read performance.

• If a table references a sequence, and the reference explicitly specifies a database name, that database cannot be renamed. In this case, you can drop the column in the table that references the sequence, or you can modify the reference so that it does not specify the database name.

• New in v20.2 By default, you cannot create sequences that are owned by columns in tables in other databases. You can enable such sequence creation by setting the sql.cross_db_sequence_owners.enabled cluster setting to true.

Required privileges

The user must have the CREATE privilege on the parent database.

Synopsis

Parameters

Sequence functions

We support the following SQL sequence functions:

• nextval('seq_name')
• currval('seq_name')
• lastval()
• setval('seq_name', value, is_called)

Temporary sequences

CockroachDB supports session-scoped temporary sequences. Unlike persistent sequences, temporary sequences can only be accessed from the session in which they were created, and they are dropped at the end of the session. You can create temporary sequences on both persistent tables and temporary tables.

Details

• Temporary sequences are automatically dropped at the end of the session.
• A temporary sequence can only be accessed from the session in which it was created.
• Temporary sequences persist across transactions in the same session.
• Temporary sequences cannot be converted to persistent sequences.

Usage

To create a temporary sequence, add TEMP/TEMPORARY to a CREATE SEQUENCE statement.

For example:

> SET experimental_enable_temp_tables=on;

> CREATE TEMP SEQUENCE temp_seq START 1 INCREMENT 1;

> SHOW CREATE temp_seq;

  table_name |                                     create_statement
-------------+--------------------------------------------------------------------------------------------
  temp_seq   | CREATE TEMP SEQUENCE temp_seq MINVALUE 1 MAXVALUE 9223372036854775807 INCREMENT 1 START 1
(1 row)

Examples

Create a sequence with default settings

In this example, we create a sequence with default settings.

> CREATE SEQUENCE customer_seq;

> SHOW CREATE customer_seq;

   table_name  |                                     create_statement
---------------+-------------------------------------------------------------------------------------------
  customer_seq | CREATE SEQUENCE customer_seq MINVALUE 1 MAXVALUE 9223372036854775807 INCREMENT 1 START 1
(1 row)

Use a sequence when creating a table

In this example, we create a table, using the nextval() function for a default value, with the customer_seq sequence as its input:

CREATE TABLE customers (
    uid UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    rownum INT DEFAULT nextval('customer_seq'),
    name STRING
);

Inserting into this table with an INSERT statement that relies on default values will call nextval, which increments the sequence.

> INSERT INTO customers (name) VALUES ('Max'), ('Alice');

> SELECT * FROM customers;

                  uid                  | rownum | name
---------------------------------------+--------+--------
  1c7f5b79-88c4-49ec-b40b-6098d28bb822 |      2 | Alice
  7ce844af-6a3f-4c52-ba07-25623f345804 |      1 | Max
(2 rows

View the current value of a sequence

To view the current value without incrementing the sequence, use:

> SELECT * FROM customer_seq;

  last_value | log_cnt | is_called
-------------+---------+------------
           2 |       0 |   true
(1 row)

If a value has been obtained from the sequence in the current session, you can also use the currval('seq_name') function to get that most recently obtained value:

> SELECT currval('customer_seq');

  currval
-----------
        2
(1 row)

Set the next value of a sequence

In this example, we're going to change the next value of customer_seq using the setval() function. Currently, the next value will be 3 (i.e., 2 + INCREMENT 1). We will change the next value to 5.

> SELECT setval('customer_seq', 5, false);

  setval
----------
       5
(1 row)

Let's add another record to the table to check that the new record adheres to the new next value.

> INSERT INTO customers (name) VALUES ('Sam');

> SELECT * FROM customers;

                  uid                  | rownum | name
---------------------------------------+--------+--------
  19ffe03d-5eac-4a2f-8aa8-1569b998aa44 |      5 | Sam
  1c7f5b79-88c4-49ec-b40b-6098d28bb822 |      2 | Alice
  7ce844af-6a3f-4c52-ba07-25623f345804 |      1 | Max
(3 rows)

Create a sequence with user-defined settings

In this example, we create a sequence that starts at -1 and descends in increments of 2.

> CREATE SEQUENCE desc_customer_list START -1 INCREMENT -2;

> SHOW CREATE desc_customer_list;

      table_name     |                                          create_statement
---------------------+-----------------------------------------------------------------------------------------------------
  desc_customer_list | CREATE SEQUENCE desc_customer_list MINVALUE -9223372036854775808 MAXVALUE -1 INCREMENT -2 START -1
(1 row)

List all sequences

> SHOW SEQUENCES;

         sequence_schema        |   sequence_name
--------------------------------+---------------------
  public                        | customer_seq
  public                        | desc_customer_list
  pg_temp_1603124728816183000_1 | temp_seq
(3 rows)

See also

• ALTER SEQUENCE
• RENAME SEQUENCE
• DROP SEQUENCE
• SHOW CREATE
• SHOW SEQUENCES
• Functions and Operators
• Other SQL Statements
• Online Schema Changes

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