# Round a date down to a unit

Shape / columns

A variant of [Parse a date or time](https://meridian.online/operations/parse-a-date-or-time).

Truncate or bucket a date or time to the start of a unit or a fixed interval.

Page: <https://meridian.online/operations/parse-a-date-or-time/round-a-date-down-to-a-unit>

## Status

Runs as a SQL step.

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

## The DuckDB step

round a date down to the start of a unit or a fixed interval

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 result AS
SELECT order_id, date_trunc('month', order_date)::DATE AS month_start, date_trunc('week', order_date)::DATE AS week_start,
       time_bucket(INTERVAL 15 MINUTE, TIMESTAMP '2026-02-10 14:37:12') AS quarter_hour
FROM orders;
SELECT * FROM result;
SELECT CASE WHEN ((SELECT [month_start::VARCHAR, week_start::VARCHAR, quarter_hour::VARCHAR] FROM result WHERE order_id = 10) = ['2026-02-01', '2026-02-09', '2026-02-10 14:30:00'] AND (SELECT count(DISTINCT month_start) FROM result) = 2 AND (SELECT count(DISTINCT week_start) FROM result) = 6) THEN 'as expected' ELSE error('dates were not rounded down to the month, the Monday of the week and the quarter hour') 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: [`Time Bin`](https://github.com/slothflowlabs/duckle/blob/f85f8960edfb6efbf4cb89d58a7b32e16df0e867/website/docs/components.html) (read 2026-09-25)
- Duckle: [`Truncate`](https://github.com/slothflowlabs/duckle/blob/f85f8960edfb6efbf4cb89d58a7b32e16df0e867/website/docs/components.html) (read 2026-09-25)
- Ibis: [`DateTruncate`](https://github.com/ibis-project/ibis/blob/05d2b293344e86cb41c1a426071734f7e270335a/ibis/expr/operations/temporal.py) (read 2026-09-27)
- Ibis: [`TimeTruncate`](https://github.com/ibis-project/ibis/blob/05d2b293344e86cb41c1a426071734f7e270335a/ibis/expr/operations/temporal.py) (read 2026-09-27)
- Ibis: [`TimestampBucket`](https://github.com/ibis-project/ibis/blob/05d2b293344e86cb41c1a426071734f7e270335a/ibis/expr/operations/temporal.py) (read 2026-09-27)
- Ibis: [`TimestampTruncate`](https://github.com/ibis-project/ibis/blob/05d2b293344e86cb41c1a426071734f7e270335a/ibis/expr/operations/temporal.py) (read 2026-09-27)
- KNIME Analytics Platform: [`Date Rounder`](https://api.hub.knime.com/nodes/*MLgWE0ePIyskKgJJ?details=full) (read 2026-09-27)
- KNIME Analytics Platform: [`Time Rounder`](https://api.hub.knime.com/nodes/*7phhn81u4VasQR1D?details=full) (read 2026-09-27)