Db2 Sequence NEXT VALUE Guide

Db2 Sequence NEXT VALUE Guide | Generated by AI

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In IBM Db2, NEXT VALUE FOR (sometimes written as NEXTVAL) is used to retrieve the next number from a sequence object. Sequences are database objects that generate numeric values, typically used for primary keys, surrogate keys, or any case where you need unique, incrementing values.

How It Works

A sequence is created using CREATE SEQUENCE. It has attributes such as START WITH, INCREMENT BY, MAXVALUE, CYCLE (whether to wrap around), and CACHE.
Each time you call NEXT VALUE FOR sequence_name, Db2 increments the sequence and returns the new value.
Unlike identity columns, sequences are independent of any particular table. You can use them across multiple tables or applications.

Example

-- Create a sequence starting from 100, incrementing by 1
CREATE SEQUENCE my_seq
  START WITH 100
  INCREMENT BY 1
  NO CYCLE;

-- Use it in a query
SELECT NEXT VALUE FOR my_seq FROM sysibm.sysdummy1;

-- Insert into a table
INSERT INTO employees (id, name)
VALUES (NEXT VALUE FOR my_seq, 'Alice');

If you run the SELECT multiple times, you’ll get 100, 101, 102, and so on.

Key Notes

CURRVAL equivalent: Db2 also supports PREVIOUS VALUE FOR to retrieve the most recently generated value in your session.
Concurrency: Each session/thread gets unique values. Sequence values are not rolled back, even if the transaction fails, to ensure uniqueness.
Caching: If you define CACHE, Db2 pre-allocates values in memory for performance. But if the database restarts, cached values may be lost (gaps can appear).
Usage in DML: You can use NEXT VALUE FOR in INSERT, UPDATE, or SELECT statements, but not in CHECK constraints or default expressions directly (depends on Db2 version).

✅ In short: NEXT VALUE FOR in Db2 increments the sequence and gives you the next available number, ensuring uniqueness and consistency across sessions.

Would you like me to also show you how this differs from identity columns in Db2?

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