The Ultimate Guide to High Availability with MariaDB

SETVAL

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Syntax

SETVAL(sequence_name, next_value, [is_used, [round]])

Contents

  1. Syntax
  2. Description
  3. Examples
  4. See Also

Description

Set the next value to be returned for a SEQUENCE.

This function is compatible with PostgreSQL syntax, extended with the round argument.

If the is_used argument is not given or is 1 or true, then the next used value will one after the given value. If is_used is 0 or false then the next generated value will be the given value.

If round is used then it will set the round value (or the internal cycle count, starting at zero) for the sequence. If round is not used, it's assumed to be 0.

next_value must be an integer literal.

For SEQUENCE tables defined with CYCLE (see CREATE SEQUENCE) one should use both next_value and round to define the next value. In this case the current sequence value is defined to be round, next_value.

The result returned by SETVAL() is next_value or NULL if the given next_value and round is smaller than the current value.

SETVAL() will not set the SEQUENCE value to a something that is less than its current value. This is needed to ensure that SETVAL() is replication safe. If you want to set the SEQUENCE to a smaller number use ALTER SEQUENCE.

If CYCLE is used, first round and then next_value are compared to see if the value is bigger than the current value.

Internally, in the MariaDB server, SETVAL() is used to inform replicas that a SEQUENCE has changed value. The replica may get SETVAL() statements out of order, but this is ok as only the biggest one will have an effect.

SETVAL requires the INSERT privilege.

Examples

SELECT setval(foo, 42);           -- Next nextval will return 43
SELECT setval(foo, 42, true);     -- Same as above
SELECT setval(foo, 42, false);    -- Next nextval will return 42

SETVAL setting higher and lower values on a sequence with an increment of 10:

SELECT NEXTVAL(s);
+------------+
| NEXTVAL(s) |
+------------+
|         50 |
+------------+

SELECT SETVAL(s, 100);
+----------------+
| SETVAL(s, 100) |
+----------------+
|            100 |
+----------------+

SELECT NEXTVAL(s);
+------------+
| NEXTVAL(s) |
+------------+
|        110 |
+------------+

SELECT SETVAL(s, 50);
+---------------+
| SETVAL(s, 50) |
+---------------+
|          NULL |
+---------------+

SELECT NEXTVAL(s);
+------------+
| NEXTVAL(s) |
+------------+
|        120 |
+------------+

Example demonstrating round:

CREATE OR REPLACE SEQUENCE s1
  START WITH 1
  MINVALUE 1
  MAXVALUE 99
  INCREMENT BY 1 
  CACHE 20 
  CYCLE;

SELECT SETVAL(s1, 99, 1, 0);
+----------------------+
| SETVAL(s1, 99, 1, 0) |
+----------------------+
|                   99 |
+----------------------+

SELECT NEXTVAL(s1);
+-------------+
| NEXTVAL(s1) |
+-------------+
|           1 |
+-------------+

The following statement returns NULL, as the given next_value and round is smaller than the current value.

SELECT SETVAL(s1, 99, 1, 0);
+----------------------+
| SETVAL(s1, 99, 1, 0) |
+----------------------+
|                 NULL |
+----------------------+

SELECT NEXTVAL(s1);
+-------------+
| NEXTVAL(s1) |
+-------------+
|           2 |
+-------------+

Increasing the round from zero to 1 will allow next_value to be returned.

SELECT SETVAL(s1, 99, 1, 1);
+----------------------+
| SETVAL(s1, 99, 1, 1) |
+----------------------+
|                   99 |
+----------------------+

SELECT NEXTVAL(s1);
+-------------+
| NEXTVAL(s1) |
+-------------+
|           1 |
+-------------+

See Also

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