> This page location: PostgreSQL Data Types > UUID > Full Neon documentation index: https://neon.com/docs/llms.txt # PostgreSQL UUID Data Type **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: ``` 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`](https://neon.com/postgresql/postgresql-tutorial/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: ```sql 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](https://neon.com/postgresql/postgresql-tutorial/postgresql-create-table) whose [primary key](https://neon.com/postgresql/postgresql-tutorial/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: ```sql 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](https://neon.com/postgresql/postgresql-tutorial/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: ```sql 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. --- ## Related docs (PostgreSQL Data Types) - [Boolean](https://neon.com/postgresql/postgresql-tutorial/postgresql-boolean) - [CHAR, VARCHAR, and TEXT](https://neon.com/postgresql/postgresql-tutorial/postgresql-char-varchar-text) - [NUMERIC](https://neon.com/postgresql/postgresql-tutorial/postgresql-numeric) - [DOUBLE PRECISION](https://neon.com/postgresql/postgresql-tutorial/postgresql-double-precision-type) - [REAL](https://neon.com/postgresql/postgresql-tutorial/postgresql-real-data-type) - [Integer](https://neon.com/postgresql/postgresql-tutorial/postgresql-integer) - [SERIAL](https://neon.com/postgresql/postgresql-tutorial/postgresql-serial) - [DATE](https://neon.com/postgresql/postgresql-tutorial/postgresql-date) - [TIMESTAMP](https://neon.com/postgresql/postgresql-tutorial/postgresql-timestamp) - [Interval](https://neon.com/postgresql/postgresql-tutorial/postgresql-interval) - [TIME](https://neon.com/postgresql/postgresql-tutorial/postgresql-time) - [JSON](https://neon.com/postgresql/postgresql-tutorial/postgresql-json) - [HSTORE](https://neon.com/postgresql/postgresql-tutorial/postgresql-hstore) - [Array](https://neon.com/postgresql/postgresql-tutorial/postgresql-array) - [User-defined Data Types](https://neon.com/postgresql/postgresql-tutorial/postgresql-user-defined-data-types) - [Enum](https://neon.com/postgresql/postgresql-tutorial/postgresql-enum) - [XML](https://neon.com/postgresql/postgresql-tutorial/postgresql-xml-data-type) - [BYTEA](https://neon.com/postgresql/postgresql-tutorial/postgresql-bytea-data-type) - [Composite Types](https://neon.com/postgresql/postgresql-tutorial/postgresql-composite-types)