What Is Serial Data Type in PostgreSQL?


Angela Bailey

What Is Serial Data Type in PostgreSQL?

In PostgreSQL, the Serial data type is a special data type that allows you to automatically generate unique integer values for a column. It is commonly used for creating primary keys or auto-incrementing fields in database tables.

Why Use Serial Data Type?

The Serial data type provides a convenient way to generate unique identifiers without having to manually manage the values. By using Serial, you can ensure that each new record inserted into the table will have a unique identifier assigned automatically.

How Does Serial Data Type Work?

The Serial data type is actually an alias for the Integer data type with an attached sequence generator. When you define a column as Serial, PostgreSQL automatically creates a sequence and sets it as the default value for that column.

For example, let’s say you have a table called “users” with a column named “id” defined as Serial:

    name VARCHAR(50)

In this case, every time you insert a new row into the “users” table without specifying a value for the “id” column, PostgreSQL will generate a unique integer value and assign it to the “id” column.


  • The default sequence name for a Serial column is usually “table_name_column_name_seq“.
  • You can also explicitly specify your own sequence name by using the SERIAL keyword followed by SERIAL4, which uses 32-bit integers, or SERIAL8, which uses 64-bit integers.
  • The maximum value a Serial column can reach depends on the integer type used. SERIAL4 has a maximum value of 2,147,483,647 and SERIAL8 has a maximum value of 9,223,372,036,854,775,807.

Using Serial Data Type in Queries

When working with Serial columns in queries, you can treat them just like regular integer columns. For example:

-- Inserting a new row with an auto-generated id:
INSERT INTO users (name) VALUES ('John Doe');

-- Retrieving all users:
SELECT * FROM users;

-- Updating a user's name based on their id:
UPDATE users SET name = 'Jane Smith' WHERE id = 1;

-- Deleting a user based on their id:
DELETE FROM users WHERE id = 1;

In the above queries, the Serial column “id” is used just like any other integer column. PostgreSQL handles the generation of unique values behind the scenes.


The Serial data type in PostgreSQL provides an efficient and automatic way to generate unique identifiers for columns. It simplifies the process of managing primary keys or auto-incrementing fields in database tables. By using Serial, you can focus on your application logic without worrying about manually assigning unique values to each record.

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