feat(sql): add difference and non_negative_difference sql functions
Scott Anderson
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@ -52,10 +52,12 @@ ORDER BY
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- [rank](#rank)
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- [row_number](#row_number)
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- [Analytical Functions](#analytical-functions)
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{{% show-in "cloud-serverless,cloud-dedicated" %}}- [difference](#difference){{% /show-in %}}
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- [first_value](#first_value)
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- [lag](#lag)
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- [last_value](#last_value)
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- [lead](#lead)
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{{% show-in "cloud-serverless,cloud-dedicated" %}}- [non_negative_difference](#non_negative_difference){{% /show-in %}}
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- [nth_value](#nth_value)
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## Window frames
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@ -796,12 +798,71 @@ Key differences:
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## Analytical Functions
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{{% show-in "cloud-serverless,cloud-dedicated" %}}- [difference](#difference){{% /show-in %}}
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- [first_value](#first_value)
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- [lag](#lag)
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- [last_value](#last_value)
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- [lead](#lead)
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{{% show-in "cloud-serverless,cloud-dedicated" %}}- [non_negative_difference](#non_negative_difference){{% /show-in %}}
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- [nth_value](#nth_value)
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{{% show-in "cloud-serverless,cloud-dedicated" %}}
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### difference
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Returns the result of subtraction between subsequent values.
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```sql
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difference(expression)
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```
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#### Arguments
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- **expression**: Expression to operate on. Can be a numeric column or
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function, and any combination of arithmetic operators.
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##### Related functions
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[non_negative_difference](#non_negative_difference)
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{{< expand-wrapper >}}
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{{% expand "View `difference` query example" %}}
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The following example uses the {{< influxdb3/home-sample-link >}}.
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{{% influxdb/custom-timestamps %}}
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```sql
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SELECT
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time,
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room,
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temp,
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difference(temp) OVER (
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PARTITION BY room
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ORDER BY time
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) AS difference
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FROM home
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WHERE
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time >= '2022-01-01T08:00:00Z'
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AND time < '2022-01-01T11:00:00Z'
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ORDER BY room, time
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```
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| time | room | temp | difference |
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| :------------------ | :---------- | ---: | ---------: |
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| 2022-01-01T08:00:00 | Kitchen | 21.0 | |
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| 2022-01-01T09:00:00 | Kitchen | 23.0 | 2.0 |
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| 2022-01-01T10:00:00 | Kitchen | 22.7 | -0.3 |
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| 2022-01-01T08:00:00 | Living Room | 21.1 | |
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| 2022-01-01T09:00:00 | Living Room | 21.4 | 0.3 |
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| 2022-01-01T10:00:00 | Living Room | 21.8 | 0.4 |
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{{% /influxdb/custom-timestamps %}}
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{{% /expand %}}
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{{< /expand-wrapper >}}
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{{% /show-in %}}
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### first_value
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Returns the value from the first row of the window frame.
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@ -1120,6 +1181,65 @@ ORDER BY room, time
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{{% /expand %}}
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{{< /expand-wrapper >}}
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{{% show-in "cloud-serverless,cloud-dedicated" %}}
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### non_negative_difference
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Returns only non-negative results of subtraction between subsequent values.
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Negative differences return _NULL_.
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```sql
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non_negative_difference(expression)
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```
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#### Arguments
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- **expression**: Expression to operate on. Can be a numeric column or
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function, and any combination of arithmetic operators.
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##### Related functions
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[difference](#difference)
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{{< expand-wrapper >}}
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{{% expand "View `non_negative_difference` query example" %}}
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The following example uses the {{< influxdb3/home-sample-link >}}.
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{{% influxdb/custom-timestamps %}}
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```sql
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SELECT
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time,
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room,
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temp,
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non_negative_difference(temp) OVER (
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PARTITION BY room
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ORDER BY time
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) AS non_negative_difference
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FROM home
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WHERE
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time >= '2022-01-01T08:00:00Z'
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AND time < '2022-01-01T11:00:00Z'
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ORDER BY room, time
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```
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| time | room | temp | non_negative_difference |
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| :------------------ | :---------- | ---: | ----------------------: |
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| 2022-01-01T08:00:00 | Kitchen | 21.0 | |
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| 2022-01-01T09:00:00 | Kitchen | 23.0 | 2.0 |
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| 2022-01-01T10:00:00 | Kitchen | 22.7 | |
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| 2022-01-01T08:00:00 | Living Room | 21.1 | |
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| 2022-01-01T09:00:00 | Living Room | 21.4 | 0.3 |
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| 2022-01-01T10:00:00 | Living Room | 21.8 | 0.4 |
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{{% /influxdb/custom-timestamps %}}
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{{% /expand %}}
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{{< /expand-wrapper >}}
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{{% /show-in %}}
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### nth_value
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Returns the value from the row that is the nth row of the window frame
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