# trunc

[Read this page in HTML](https://www.scopedb.io/docs/reference/functions/date-and-time/temporal-trunc)

Truncates a timestamp to the start of a specified time unit.

## Syntax

```scopeql
trunc(<timestamp>, unit => <unit>)
```

## Arguments

| Argument      | Type        | Description                                                                                                              |
| ------------- | ----------- | ------------------------------------------------------------------------------------------------------------------------ |
| `<timestamp>` | `timestamp` | Timestamp to truncate.                                                                                                   |
| `unit`        | `string`    | Constant. Unit: `'hour'`, `'minute'`, `'second'`, `'millisecond'`, `'microsecond'`, or `'nanosecond'`. Must not be NULL. |

## Returns

Returns `timestamp`, rounded down to the unit boundary in UTC. Returns NULL if the input is NULL.

## Usage notes

To group by calendar day, use [`strftime`](https://www.scopedb.io/docs/reference/functions/date-and-time/format-parse.md), for example `strftime(event_time, format => '%Y-%m-%d', timezone => 'UTC')`.

## Examples

Truncate timestamps to their UTC hour before grouping. Events within the same hour share one bucket.

```scopeql
VALUES
    ('2026-06-01T10:02:00Z'), ('2026-06-01T10:48:00Z'),
    ('2026-06-01T11:05:00Z'), ('2026-06-01T11:12:00Z'), ('2026-06-01T11:56:00Z')
SELECT $0::timestamp AS event_time
GROUP BY trunc(event_time, unit => 'hour') AS hour
AGGREGATE count() AS checkouts
ORDER BY hour
```

```text
+----------------------+-----------+
| hour                 | checkouts |
+----------------------+-----------+
| 2026-06-01T10:00:00Z | 2         |
| 2026-06-01T11:00:00Z | 3         |
+----------------------+-----------+
```