ALTER SEQUENCE statement

The ALTER SEQUENCE statement can be used to change a sequence.

A sequence can be changed in the following ways:
  • Restarting the sequence
  • Changing the increment between future sequence values
  • Setting or eliminating the minimum or maximum values
  • Changing the number of cached sequence numbers
  • Changing the attribute that determines whether the sequence can cycle or not
  • Changing whether sequence numbers must be generated in order of request

Invocation

This statement can be embedded in an application program or issued through the use of dynamic SQL statements. It is an executable statement that can be dynamically prepared only if DYNAMICRULES run behavior is in effect for the package (SQLSTATE 42509).

Authorization

The privileges held by the authorization ID of the statement must include at least one of the following authorities:
  • ALTER privilege on the sequence to be altered
  • ALTERIN privilege on the schema implicitly or explicitly specified
  • SCHEMAADM authority on the schema implicitly or explicitly specified
  • DBADM authority

Syntax

Read syntax diagramSkip visual syntax diagramALTER SEQUENCEsequence-name1RESTARTWITHnumeric-constantINCREMENT BYnumeric-constantMINVALUEnumeric-constantNO MINVALUEMAXVALUEnumeric-constantNO MAXVALUECYCLENO CYCLECACHEinteger-constantNO CACHEORDERNO ORDER
Notes:
  • 1 The same clause must not be specified more than once.

Description

sequence-name
Identifies the sequence that is to be changed. The name, including the implicit or explicit schema qualifier, must uniquely identify an existing sequence at the current server. If no sequence by this name exists in the explicitly or implicitly specified schema, an error (SQLSTATE 42704) is returned. sequence-name must not be a sequence generated by the system for an identity column (SQLSTATE 428FB).
RESTART
Restarts the sequence. If numeric-constant is not specified, the sequence is restarted at the value specified implicitly or explicitly as the starting value on the CREATE SEQUENCE statement that originally created the sequence.
WITH numeric-constant
Restarts the sequence with the specified value. This value can be any positive or negative value that could be assigned to a column of the data type associated with the sequence (SQLSTATE 42815), without nonzero digits existing to the right of the decimal point (SQLSTATE 428FA).
INCREMENT BY numeric-constant
Specifies the interval between consecutive values of the sequence. This value can be any positive or negative value that could be assigned to a column of the data type associated with the sequence (SQLSTATE 42815). The value must not exceed the value of a large integer constant (SQLSTATE 42820) and must not contain nonzero digits to the right of the decimal point (SQLSTATE 428FA).

If this value is negative, then this is a descending sequence. If this value is 0 or positive, this is an ascending sequence after the ALTER statement.

MINVALUE or NO MINVALUE
Specifies the minimum value at which a descending sequence either cycles or stops generating values, or an ascending sequence cycles to after reaching the maximum value.
MINVALUE numeric-constant
Specifies the numeric constant that is the minimum value. This value can be any positive or negative value that could be assigned to a column of the data type associated with the sequence (SQLSTATE 42815), without nonzero digits existing to the right of the decimal point (SQLSTATE 428FA), but the value must be less than or equal to the maximum value (SQLSTATE 42815).
NO MINVALUE
For an ascending sequence, the value is the original starting value. For a descending sequence, the value is the minimum value of the data type associated with the sequence.
MAXVALUE or NO MAXVALUE
Specifies the maximum value at which an ascending sequence either cycles or stops generating values, or a descending sequence cycles to after reaching the minimum value.
MAXVALUE numeric-constant
Specifies the numeric constant that is the maximum value. This value can be any positive or negative value that could be assigned to a column of the data type associated with the sequence (SQLSTATE 42815), without nonzero digits existing to the right of the decimal point (SQLSTATE 428FA), but the value must be greater than or equal to the minimum value (SQLSTATE 42815).
NO MAXVALUE
For an ascending sequence, the value is the maximum value of the data type associated with the sequence. For a descending sequence, the value is the original starting value.
CYCLE or NO CYCLE
Specifies whether the sequence should continue to generate values after reaching either its maximum or minimum value. The boundary of the sequence can be reached either with the next value landing exactly on the boundary condition, or by overshooting the value.
CYCLE
Specifies that values continue to be generated for this sequence after the maximum or minimum value has been reached. If this option is used, after an ascending sequence reaches its maximum value, it generates its minimum value; or after a descending sequence reaches its minimum value, it generates its maximum value. The maximum and minimum values for the sequence determine the range that is used for cycling.

When CYCLE is in effect, then duplicate values can be generated for the sequence.

NO CYCLE
Specifies that values will not be generated for the sequence once the maximum or minimum value for the sequence has been reached.
CACHE or NO CACHE
Specifies whether to keep some preallocated values in memory for faster access. This is a performance and tuning option.
CACHE integer-constant
Specifies the maximum number of sequence values that are preallocated and kept in memory. Preallocating and storing values in the cache reduces synchronous I/O to the log when values are generated for the sequence.
In the event of a system failure, all cached sequence values that have not been used in committed statements are lost (that is, they will never be used).The maximum number of sequence values that can be lost is calculated as follows:
  • If ORDER is specified, the maximum is the value specified for the CACHE option.
  • In a multi-partition environment, the maximum is the value specified for the CACHE option times the number of members that generate new identity values.

The minimum value is 2 (SQLSTATE 42815).

NO CACHE
Specifies that values of the sequence are not to be preallocated. It ensures that there is not a loss of values in the case of a system failure, shutdown or database deactivation. When this option is specified, the values of the sequence are not stored in the cache. In this case, every request for a new value for the sequence results in synchronous I/O to the log.
ORDER or NO ORDER
Specifies whether the sequence numbers must be generated in order of request.
ORDER
Specifies that the sequence numbers are generated in order of request.
NO ORDER
Specifies that the sequence numbers do not need to be generated in order of request.

Notes

  • Only future sequence numbers are affected by the ALTER SEQUENCE statement.
  • The data type of a sequence cannot be changed. Instead, drop and re-create the sequence specifying the required data type for the new sequence.
  • All cached values are lost when a sequence is altered.
  • After restarting a sequence or changing to CYCLE, it is possible for sequence numbers to be duplicate values of ones generated by the sequence previously.

Example

A possible reason for specifying RESTART without a numeric value would be to reset the sequence to the START WITH value. In this example, the goal is to generate the numbers from 1 up to the number of rows in the table and then inserting the numbers into a column added to the table using temporary tables. Another use would be to get results back where all the resulting rows are numbered: 
   ALTER SEQUENCE ORG_SEQ RESTART
   SELECT NEXT VALUE FOR ORG_SEQ, ORG.* FROM ORG