> For the complete documentation index, see [llms.txt](https://docs.postgresql.tw/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.postgresql.tw/the-sql-language/datatype/datatype-uuid.md). # 8.12. UUID Type \# The data type `uuid` stores Universally Unique Identifiers (UUID) as defined by [RFC 9562](https://datatracker.ietf.org/doc/html/rfc9562), ISO/IEC 9834-8:2005, and related standards. (Some systems refer to this data type as a globally unique identifier, or GUID, instead.) This identifier is a 128-bit quantity that is generated by an algorithm chosen to make it very unlikely that the same identifier will be generated by anyone else in the known universe using the same algorithm. Therefore, for distributed systems, these identifiers provide a better uniqueness guarantee than sequence generators, which are only unique within a single database. RFC 9562 defines 8 different UUID versions. Each version has specific requirements for generating new UUID values, and each version provides distinct benefits and drawbacks. PostgreSQL provides native support for generating UUIDs using the UUIDv4 and UUIDv7 algorithms. Alternatively, UUID values can be generated outside of the database using any algorithm. The data type `uuid` can be used to store any UUID, regardless of the origin and the UUID version. A UUID is written as a sequence of lower-case hexadecimal digits, in several groups separated by hyphens, specifically a group of 8 digits followed by three groups of 4 digits followed by a group of 12 digits, for a total of 32 digits representing the 128 bits. An example of a UUID in this standard form is: ``` a0eebc99-9c0b-4ef8-bb6d-6bb9bd380a11 ``` PostgreSQL also accepts the following alternative forms for input: use of upper-case digits, the standard format surrounded by braces, omitting some or all hyphens, adding a hyphen after any group of four digits. Examples are: ``` A0EEBC99-9C0B-4EF8-BB6D-6BB9BD380A11 {a0eebc99-9c0b-4ef8-bb6d-6bb9bd380a11} a0eebc999c0b4ef8bb6d6bb9bd380a11 a0ee-bc99-9c0b-4ef8-bb6d-6bb9-bd38-0a11 {a0eebc99-9c0b4ef8-bb6d6bb9-bd380a11} ``` Output is always in the standard form. See [Section 9.14](/the-sql-language/functions/functions-uuid.md) for how to generate a UUID in PostgreSQL. *** 原文：[PostgreSQL 18.6 Documentation](https://www.postgresql.org/docs/18/datatype-uuid.html)（英文原文，待翻譯） --- # 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, and the optional `goal` query parameter: ``` GET https://docs.postgresql.tw/the-sql-language/datatype/datatype-uuid.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. 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.