When working with sequences in PostgreSQL, we have the flexibility to choose between creating a non-repeating sequence or a repeating sequence. It totally depends on the user’s requirements. A repeating sequence, as the name itself suggests, cycles through its values once it reaches its maximum or minimum values and starts over again. While the non-repeating sequence follows a linear progression and stops its execution when it reaches its maximum or minimum value.

This comprehensive guide demonstrates how to create a repeating sequence in Postgres.

Creating a Repeating Sequence in PostgreSQL: A Comprehensive Guide

Creating a repeating sequence in Postgres guarantees that the previously generated sequence numbers can be reused, which means a repeating sequence can repeat indefinitely. While a non-repeating sequence follows a linear progression and hence generates unique values without any repetition.

Syntax

To create a repeating sequence in Postgres, the CREATE SEQUENCE command can be executed with the “CYCLE” option enabled. Here is the syntax for creating a repeating sequence in Postgres:

CREATE SEQUENCE Seq_name
MAXVALUE maximum_value
CYCLE;

Let's delve into practical implementation to gain a deeper understanding of this concept.

Example 1: Creating an Ascending Repeating Sequence

The following example creates an ascending repeating sequence starting from 1, ending at 5, and incremented by 2 on each iteration:

CREATE SEQUENCE cp_sequence
START 1
INCREMENT 2
MAXVALUE 5
CYCLE;

Now utilize the nextval() function to see how repeating sequence works in Postgres:

SELECT nextval('cp_sequence')
UNION ALL
SELECT nextval('cp_sequence')
UNION ALL
SELECT nextval('cp_sequence')
UNION ALL
SELECT nextval('cp_sequence')
UNION ALL
SELECT nextval('cp_sequence');

The output demonstrates that the sequence restarted when it reaches its maximum limit.

Example 2: Creating a Descending Repeating Sequence

In the following example, we will show you how to create a descending repeating sequence in Postgres:

CREATE SEQUENCE cp_seq
START 0
INCREMENT -2
MINVALUE -10
MAXVALUE 0
CYCLE;

Let’s utilize the nextval() function to see how descending repeating sequence works in Postgres:

SELECT nextval('cp_seq')
UNION ALL
SELECT nextval('cp_seq')
UNION ALL
SELECT nextval('cp_seq')
UNION ALL
SELECT nextval('cp_seq')
UNION ALL
SELECT nextval('cp_seq')
UNION ALL
SELECT nextval('cp_seq');

That’s all about creating an ascending or descending repeating sequence in Postgres.

Conclusion

To create a repeating sequence in Postgres, the CREATE SEQUENCE command can be executed with the “CYCLE” option enabled. Creating a repeating sequence in Postgres guarantees that the previously generated sequence numbers can be reused, which means a repeating sequence can repeat indefinitely. This post has explained how to create an ascending or descending repeating sequence in Postgres.