> ## Documentation Index
> Fetch the complete documentation index at: https://www.integrate.io/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# ETL: ISOToHour

> Truncate an ISO datetime string to the start of its hour. Use ISOTOHOUR for hourly aggregations and time bucketing in ETL pipeline expressions.

## Description

Resets the ISO datetime string to the beginning of the hour specified in the string.

## Syntax

`ISOToHour(datetime_string)`

## Examples

`ISOToHour('2009-01-07T01:07:01.000Z')` returns 2009-01-07T01:00:00.000Z

## Notes

The datetime\_string must be in ISO 8601 date time format, otherwise the job will fail. See [Using ISO 8601 date/time functions](/etl/using-iso-8601-string-functions/).

## Return value datatype

String

## Impact of null value

If input is null, returns null.