Generates a random UUID — a unique identifier like 3f2c9a1e-….
GEN_RANDOM_UUID()
Returns a version 4 UUID: 32 randomly generated hexadecimal digits with hyphens. The chance of two identical ones is negligible, so such keys can be created anywhere — in the database or in the application — without coordination. Most often they're used as a default value: id uuid PRIMARY KEY DEFAULT gen_random_uuid().
employees
| name | department | salary | bonus | phone |
|---|---|---|---|---|
| Emma | backend | 1200 | 300 | +44 7700 900123 |
| Liam | backend | 1000 | NULL | NULL |
| Olivia | frontend | 1350 | 150 | +44 7700 900456 |
| Noah | frontend | 950 | NULL | +44 7700 900789 |
| Sophia | design | 1200 | 200 | NULL |
These tables already exist in the sandbox — the examples below use them. Want to try this in your own database? Copy the SQL.
| id |
|---|
| f9b34e8f-3f5a-45cf-b0b1-0c6add1723b7 |
The result is different every time — press “Run” again.
| name | id |
|---|---|
| Emma | 8163699d-3f38-4465-906f-9694ee1361ef |
| Liam | 465e8725-8440-4db0-9447-541a2edbccb4 |
| Olivia | 6a504341-3ea7-496d-a870-3be957a3864c |
| Noah | a1749abe-3d3c-4cd7-9dac-4a5ea254f914 |
| Sophia | c4a4a7e9-c8be-4e1a-b747-239b0ca0262d |
| type | text_length |
|---|---|
| uuid | 36 |
Store it as uuid, not text: as uuid it takes 16 bytes, while as text it's 36 characters with slower comparisons.
Random UUIDs aren't ordered by creation time: ORDER BY id won't give you insertion order, and new values are scattered across the whole index. PostgreSQL 18 has uuidv7(), which puts the time at the beginning.
A UUID takes 16 bytes versus 8 for a bigint. For huge tables with many relationships, that's noticeable in index size.