---
title: 'PostgreSQL UUID Data Type'
page_title: 'PostgreSQL UUID Data Type'
page_description: 'In this tutorial, you will learn how to use PostgreSQL UUID data type and how to generate UUID values using the gen_random_uuid() function.'
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updatedOn: '2024-02-01T09:53:47+00:00'
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---

**Summary**: in this tutorial, you will learn about the PostgreSQL UUID data type and how to generate UUID values using a supplied module.

## Introduction to PostgreSQL UUID type

UUID stands for Universal Unique Identifier defined by [RFC 4122](https://tools.ietf.org/html/rfc4122 'UUID') and other related standards.

A UUID value is a 128\-bit quantity generated by an algorithm that makes it unique in the known universe using the same algorithm.

The following shows some examples of UUID values:

```sql
40e6215d-b5c6-4896-987c-f30f3678f608
6ecd8c99-4036-403d-bf84-cf8400f67836
3f333df6-90a4-4fda-8dd3-9485d27cee36
```

A UUID is a sequence of 32 digits of hexadecimal digits represented in groups separated by hyphens.

Because of its uniqueness feature, you often find UUID in distributed systems because it guarantees a better uniqueness than the [`SERIAL`](postgresql-serial) data type which generates unique values within a single database.

To store UUID values in the PostgreSQL database, you use the UUID data type.

## Generating UUID values

PostgreSQL provides you with a function to generate a UUID:

```sql
gen_random_uuid()
```

The `gen_random_uuid()` function returns a version 4 (random) UUID. For example:

```
SELECT gen_random_uuid();
```

Output:

```
           gen_random_uuid
--------------------------------------
 d6eb621f-6dd0-4cdc-93f5-07f51b249b51
(1 row)
```

## Creating a table with a UUID column

We will [create a table](postgresql-create-table) whose [primary key](postgresql-primary-key) is a UUID data type. Additionally, the values of the primary key column will be generated automatically using the `gen_random_uuid()` function.

First, create the `contacts` table:

```
CREATE TABLE contacts (
    contact_id uuid DEFAULT gen_random_uuid(),
    first_name VARCHAR NOT NULL,
    last_name VARCHAR NOT NULL,
    email VARCHAR NOT NULL,
    phone VARCHAR,
    PRIMARY KEY (contact_id)
);
```

In this statement, the data type of the `contact_id` column is `UUID`.

The `contact_id` column has a default value provided by the `gen_random_uuid()` function, therefore, whenever you insert a new row without specifying the value for the contact_id `column`, PostgreSQL will call the `gen_random_uuid()` function to generate the value for it.

Second, [insert](postgresql-insert) some data into the `contacts` table:

```sql
INSERT INTO contacts ( first_name, last_name, email, phone)
VALUES
  ('John', 'Smith', 'john.smith@example.com',  '408-237-2345'),
  ('Jane', 'Smith', 'jane.smith@example.com', '408-237-2344'),
  ('Alex', 'Smith', 'alex.smith@example.com', '408-237-2343')
RETURNING *;
```

Output:

```text
              contact_id              | first_name | last_name |         email          |    phone
--------------------------------------+------------+-----------+------------------------+--------------
 ca61da8c-938a-48a6-8eb6-55aa08cd1b08 | John       | Smith     | john.smith@example.com | 408-237-2345
 fe2af584-8576-4d0e-b10d-6ec970732f8e | Jane       | Smith     | jane.smith@example.com | 408-237-2344
 141aefe8-f553-43b9-bfbf-91361e83b15e | Alex       | Smith     | alex.smith@example.com | 408-237-2343
(3 rows)

```

The output indicates that the `contact_id` column has been populated by the UUID values generated by the `gen_random_uuid()` function.

## Using uuid\-ossp module in the old version of PostgreSQL

If you use an old version of PostgreSQL, you need to use a third\-party module [uuid\-ossp](https://www.postgresql.org/docs/16/uuid-ossp.html) that provides specific algorithms to generate UUIDs

To install the `uuid-ossp` module, you use the `CREATE EXTENSION` statement as follows:

```
CREATE EXTENSION IF NOT EXISTS "uuid-ossp";
```

The `IF NOT EXISTS` clause allows you to avoid re\-installing the module.

If you want to generate a UUID value, you can use the `uuid_generate_v4()` function. For example:

```sql
SELECT uuid_generate_v4();
```

Output:

```
           uuid_generate_v4
--------------------------------------
 351c1afe-21b2-486c-951b-66bc9e852530
(1 row)
```

For more information on the functions for UUID generation, check out the [uuid\-ossp](https://www.postgresql.org/docs/9.5/static/uuid-ossp.html) module documentation.

## Summary

- UUID stands for Universal Unique Identifier.
- Use the `gen_random_uuid()` function to generate a version 4 (random) UUID.