> For the complete documentation index, see [llms.txt](https://dev-notes.vinguyen.blog/notes/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://dev-notes.vinguyen.blog/notes/deployment-and-operation/database/postgresql/postgresql-create-a-new-primary-key-auto-increment-column.md).

# PostgreSQL - Create a new primary key auto-increment column

**Method 1: Using the `SERIAL` data type (Pre-PostgreSQL 10):**

```sql
-- Assuming you have an existing table called "your_table"
-- Add an auto-increment column named "id" using SERIAL
ALTER TABLE your_table
ADD COLUMN id SERIAL PRIMARY KEY;
```

This command adds a new column named "id" to the existing table and sets it as the primary key with an auto-increment feature using the `SERIAL` data type.

**Method 2: Using the `GENERATED` column feature (PostgreSQL 12 and later):**

```sql
-- Assuming you have an existing table called "your_table"
-- Add an auto-increment column named "id" using GENERATED ALWAYS AS IDENTITY
ALTER TABLE your_table
ADD COLUMN id INT GENERATED ALWAYS AS IDENTITY PRIMARY KEY;
```


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://dev-notes.vinguyen.blog/notes/deployment-and-operation/database/postgresql/postgresql-create-a-new-primary-key-auto-increment-column.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.