How to Reset the Primary Key Sequence ID in PostgreSQL?

PostgreSQL is a powerful, open-source, object-relational database management system (DBMS) developed by a community of contributors. primary key in PostgreSQL is a unique identifier for each row in a table. It is a column or a combination of columns that ensures the integrity of the data in the table. In this article, we will explore how to Reset the Primary Key Sequence ID with the help of different approaches & we will also see examples of each approach.

How to Reset the Primary Key Sequence ID in PostgreSQL?

When working with PostgreSQL process of Resetting the Primary Key Sequence ID. There are a few different approaches to resetting the primary key sequence ID in PostgreSQL, each with its advantages and disadvantages. The following approaches are:

1. Using the ALTER SEQUENCE Command
   
2. Using SETVAL and pg_get_serial_sequence

Before we delve deeper into the queries, let's create the table courses in gfg database and insert some sample values in the table. The following code creates the Sample Table and inserts the entries in the table.

CREATE DATABASE gfg;
-- Create a table
CREATE TABLE courses (
    course_id SERIAL PRIMARY KEY,
    course_name VARCHAR(100),
    fees DECIMAL(10, 2),
    instructor VARCHAR(100)
);

-- Insert some sample data
INSERT INTO courses (course_id,course_name, fees, instructor) 
VALUES 
    (1,'Java', 10000, 'Akhil'),
    (2,'Python', 15000, 'Jacky'),
    (3,'C++', 20000, 'Sourav');

Output:

1. Using the ALTER SEQUENCE Command

The ALTER SEQUENCE command in PostgreSQL is used to modify the properties of a sequence. Sequences are database objects that generate unique sequential numbers, typically used as primary key values.

Syntax:

ALTER SEQUENCE name [ INCREMENT [ BY ] increment ]
    [ START [ WITH ] start ]
    [ MINVALUE minvalue | NO MINVALUE ]
    [ MAXVALUE maxvalue | NO MAXVALUE ]
    [ CACHE ]
    [ CYCLE | NO CYCLE ]
    [ OWNED BY { table_name.column_name | NONE } ];

• name: is the name of the sequence object to be altered.
• increment: is the increment value for the sequence. If omitted, the increment value is 1.
• start: is the start value for the sequence. If omitted, the start value is the current value of the sequence.
• minvalue and maxvalue: specify the minimum and maximum values for the sequence, respectively. If omitted, the minimum and maximum values are determined by the integer, bigint, or smallint data type of the sequence.
• cache: specifies the cache size for the sequence. If omitted, the cache size is set to the default value.
• cycle: specifies that the sequence should cycle after reaching its maximum value. If omitted, the sequence does not cycle.
• owned by: specifies the table and column that own the sequence. If omitted, the sequence is owned by no table or column

Example

The following query reset the sequence to start from the next value after the maximum course_id. Assuming the sequence name is courses_course_id_seq and returns the result as before:

ALTER SEQUENCE courses_course_id_seq RESTART WITH 5;

The above query, resets the auto-increment sequence for the course_id column in the courses table to start from 5,.

Output:

2. Using SETVAL and pg_get_serial_sequence:

The setval() function in PostgreSQL is used to set the value of a sequence.

Syntax:

SETVAL(sequence_name, next_value)

• sequence_name: is the name of the sequence you want to set the value for.
• next_value: is the new value you want to set the sequence to.

Example

The following query reset the primary key sequence ID in PostgreSQL, you can use the SETVAL function along with pg_get_serial_sequence.

-- Find the name of the sequence
SELECT pg_get_serial_sequence('courses', 'course_id');

-- Reset the sequence
SELECT setval('courses_course_id_seq', (SELECT MAX(course_id)+1 FROM courses));

In the above query, SELECT pg_get_serial_sequence('courses', 'course_id'); retrieves the name of the sequence associated with the course_id column in the courses table, and the second line SELECT setval('courses_course_id_seq', (SELECT MAX(course_id)+1 FROM courses)); resets the courses_course_id_seq sequence to start from the next value after the current maximum course_id in the courses table.

Output:

Conclusion

In this article, we covered How to Reset the Primary Key Sequence ID in PostgreSQL. with the help of two method, first one is  the ALTER SEQUENCE  command. We understood the example of the ALTER SEQUENCE  command. We later looked at Using SETVAL and pg_get_serial_sequence functions and understood the ease it provide. so now you can effectively reset the primary key sequence ID in PostgreSQL and maintain the integrity of your database.