# Add a unique id

Shape / rows

A variant of [Number or rank rows](https://meridian.online/operations/number-or-rank-rows).

Add a column holding a random, hashed or time-ordered identifier that is unique to each row and does not depend on row order.

Page: <https://meridian.online/operations/number-or-rank-rows/add-a-unique-id>

## Status

Runs as a SQL step.

arcform carries it as a `sql:` step today.

## The DuckDB step

add a random, hashed or time-ordered identifier to each row

It reads the `orders` table the proofs share. Create it first:

```sql
CREATE TABLE orders AS SELECT * FROM (VALUES
  (1,  'Alice Ng',      'north', DATE '2026-01-03', 120.00, 'widget', 'a|b',   '{"channel":"web","items":[1,2]}'),
  (2,  'alice ng',      'north', DATE '2026-01-05',  80.50, 'gadget', 'b',     '{"channel":"shop","items":[3]}'),
  (3,  'Bob  Okafor',   'south', DATE '2026-01-05', 300.00, 'widget', 'a|c',   '{"channel":"web","items":[4,5,6]}'),
  (4,  'Carla Díaz',    'east',  DATE '2026-01-09',  NULL,  'gizmo',  NULL,    '{"channel":"web","items":[]}'),
  (5,  'Bob Okafor',    'south', DATE '2026-01-12',  45.25, 'gadget', 'c',     '{"channel":"phone","items":[7]}'),
  (6,  'Dev Patel',     'west',  DATE '2026-01-12', 510.00, 'widget', 'a',     '{"channel":"web","items":[8,9]}'),
  (7,  'Carla Diaz',    'east',  DATE '2026-01-20',  99.99, 'gizmo',  'b|c',   '{"channel":"shop","items":[10]}'),
  (8,  'Dev Patel',     'west',  DATE '2026-02-02', 510.00, 'widget', 'a',     '{"channel":"web","items":[8,9]}'),
  (9,  'Eve Larsen',    NULL,    DATE '2026-02-03',  15.00, 'gadget', NULL,    '{"channel":"web","items":[11]}'),
  (10, 'Alice Ng',      'north', DATE '2026-02-10', 220.00, 'gizmo',  'a|b|c', '{"channel":"phone","items":[12,13]}')
) t(order_id, customer, region, order_date, amount, product, tags, meta);
```

Then run the statement:

```sql
CREATE TEMP TABLE with_ids AS
SELECT order_id, customer,
       uuid() AS random_id,
       md5(order_id::VARCHAR) AS hashed_id,
       uuidv7() AS time_id
FROM orders o;
-- the hashed id is the md5 of the key, which is unique because order_id is; it depends on the key and not on row order, so reading the rows in another order gives the same ids
CREATE TEMP TABLE reordered AS
SELECT order_id, md5(order_id::VARCHAR) AS hashed_id FROM (SELECT * FROM orders ORDER BY order_id DESC) o;
SELECT order_id, hashed_id FROM with_ids ORDER BY order_id;
SELECT CASE WHEN ((SELECT count(DISTINCT random_id) = 10 AND count(DISTINCT hashed_id) = 10 AND count(DISTINCT time_id) = 10 FROM with_ids) AND (SELECT bool_and(length(random_id::VARCHAR) = 36 AND length(hashed_id) = 32) FROM with_ids) AND (SELECT bool_and(substr(time_id::VARCHAR, 15, 1) = '7' AND uuid_extract_timestamp(time_id) > now() - INTERVAL 1 HOUR) FROM with_ids) AND (SELECT count(*) FROM with_ids w JOIN reordered r USING (order_id, hashed_id)) = 10) THEN 'as expected' ELSE error('the random, hashed and time-ordered ids were not ten distinct values each, or the hashed id changed with row order') END AS verdict;
```

It needs nothing installed beyond DuckDB itself.

## What other tools call it

Meridian's classification; an independent blind rating agreed on 95.7% of 324 rows (variant, version 3).

- Duckle: [`Surrogate Key`](https://github.com/slothflowlabs/duckle/blob/f85f8960edfb6efbf4cb89d58a7b32e16df0e867/frontend/src/workflow-ui/palette-data.ts) (read 2026-09-25)
- Duckle: [`UUID`](https://github.com/slothflowlabs/duckle/blob/f85f8960edfb6efbf4cb89d58a7b32e16df0e867/website/docs/components.html) (read 2026-09-25)
- EasyMorph: [`Generate unique identifiers`](https://help.easymorph.com/doku.php?id=transformations:generateuids) (read 2026-09-27)
- AWS Glue: [`UUID`](https://docs.aws.amazon.com/glue/latest/dg/transforms-uuid.html) (read 2026-09-27)
- Apache Hop: [`Snowflake ID Generator`](https://hop.apache.org/manual/latest/pipeline/transforms/snowflakeid.html) (read 2026-09-27)
- Ibis: [`RandomUUID`](https://github.com/ibis-project/ibis/blob/05d2b293344e86cb41c1a426071734f7e270335a/ibis/expr/operations/generic.py) (read 2026-09-27)