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Documentation for DATETRUNC #10756

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67 changes: 66 additions & 1 deletion content/en/docs/refguide/modeling/domain-model/oql/oql-expression-syntax.md
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Original file line number Diff line number Diff line change
Expand Up @@ -687,6 +687,7 @@ These are the currently supported functions:
* COALESCE
* DATEDIFF
* DATEPART
* DATETRUNC
* LENGTH
* LOWER
* RANGEBEGIN
Expand Down Expand Up @@ -875,7 +876,7 @@ DATEDIFF ( unit , startdate_expression, enddate_expression [, timezone ] )
* `MINUTE`,
* `SECOND`
* `MILLISECOND`.

For more information on `DATETIME` values, see the [example section under *DATEPART*](#oql-datepart-example), below.

##### startdate_expression
Expand Down Expand Up @@ -981,6 +982,70 @@ SELECT End FROM Sales.Period WHERE DATEPART(YEAR, End) = 2025
|---------------------|
| 2025-07-05 00:00:00 |

### DATETRUNC {#datetrunc-function}

The `DATETRUNC` function truncates a `DATETIME` value to a specified datepart. The return type is `DATETIME`.

This function was introduced in Mendix version 11.9.0

#### Syntax

The syntax is as follows:

```sql
DATETRUNC ( datepart , date_expression [, timezone ] )
```

##### datepart

`datepart` specifies the part to which the `DATETIME` value is truncated. For possible values, see the [Example](#oql-datetrunc-example) below.

##### date_expression

`date_expression` specifies the date to retrieve an element from. The expression should resolve to a `DATETIME` value. String representations of `DATETIME` are accepted.

##### timezone

`timezone` specifies the time zone to use for truncation. This parameter is optional and defaults to the local time zone. It should be a string literal containing an IANA time zone. GMT offset time zones are not supported.
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@basdebakker basdebakker Feb 17, 2026

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The phrase "local time zone" is used in many places, but I think it is unclear what that means. "user time zone" may be better, possibly with a link to https://docs.mendix.com/refguide/date-and-time-handling/.

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@basdebakker basdebakker Feb 17, 2026

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I think it would be good to mention the option of using 'UTC' explicitly.


#### Examples{#oql-datetrunc-example}

| datepart | Truncation result for `2005-09-03T16:34:20.356` |
|--------------|-------------------------------------------------|
| `YEAR` | `2005-01-01T00:00:00.000` |
| `QUARTER` | `2005-07-01T00:00:00.000` |
| `MONTH` | `2005-09-01T00:00:00.000` |
| `DAY` | `2005-09-03T00:00:00.000` |
| `WEEK`* | `2005-07-29T00:00:00.000` |
| `HOUR` | `2005-09-03T16:00:00.000` |
| `MINUTE` | `2005-09-03T16:34:00.000` |
| `SECOND` | `2005-09-03T16:34:20.000` |

{{% alert color="info" %}}
Date part types `DAYOFYEAR`, `WEEKDAY` and `MILLISECOND` are not supported by the `DATETRUNC` function
{{% /alert %}}

{{% alert color="info" %}}
For the date part type `WEEK`, the result of the `DATETRUNC` function depends on the database configuration. For example, by default, the first day of the week in MS SQL Server is Sunday, which means that dates are truncated to previos Sunday if date part type `WEEK` is used.
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@basdebakker basdebakker Feb 17, 2026

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Typo in previo[u]s.

{{% /alert %}}

`DATETRUNC` function can be used to group data by time periods:

```sql
SELECT
DATETRUNC(QUARTER, End) AS PeriodEndQuarter,
SUM(Revenue) AS QuarterPeriodRevenue
FROM
Sales.Period
GROUP BY
DATETRUNC(QUARTER, End)
```

| PeriodEndQuarter | QuarterPeriodRevenue |
|---------------------|----------------------|
| 2024-04-01 00:00:00 | 10 |
| 2025-07-01 00:00:00 | 28 |

### LENGTH {#length-function}

#### Description
Expand Down