276 lines
7.6 KiB
Markdown
276 lines
7.6 KiB
Markdown
The {{< product-name >}} SQL implementation supports the following miscellaneous functions
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for performing a variety of operations:
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- [arrow_cast](#arrow_cast)
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- [arrow_typeof](#arrow_typeof)
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- [get_field](#get_field)
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- [interpolate](#interpolate)
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- [locf](#locf)
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- [version](#version)
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## arrow_cast
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Casts a value to a specific Arrow data type.
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```sql
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arrow_cast(expression, datatype)
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```
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### Arguments
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- **expression**: Expression to cast.
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Can be a constant, column, or function, and any combination of arithmetic or
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string operators.
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- **datatype**: [Arrow data type](/influxdb/version/reference/sql/data-types/#sql-and-arrow-data-types)
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to cast to.
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{{< expand-wrapper >}}
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{{% expand "View `arrow_cast` query example" %}}
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_The following example uses the sample data set provided in
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[Get started with InfluxDB tutorial](/influxdb/version/get-started/write/#construct-line-protocol)._
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```sql
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SELECT
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arrow_cast(time, 'Int64') AS time,
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arrow_cast(temp, 'Utf8') AS temp,
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arrow_cast(co, 'Float64')AS co
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FROM home
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LIMIT 1
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```
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| time | temp | co |
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| :------------------ | ---: | --: |
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| 1641024000000000000 | 21.0 | 0 |
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{{% /expand %}}
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{{< /expand-wrapper >}}
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## arrow_typeof
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Returns the underlying [Arrow data type](https://arrow.apache.org/datafusion/user-guide/sql/data_types.html)
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of the expression:
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```sql
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arrow_typeof(expression)
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```
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### Arguments
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- **expression**: Expression to evaluate.
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Can be a constant, column, or function, and any combination of arithmetic or
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string operators.
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{{< expand-wrapper >}}
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{{% expand "View `arrow_typeof` query example" %}}
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_The following example uses the sample data set provided in
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[Get started with InfluxDB tutorial](/influxdb/version/get-started/write/#construct-line-protocol)._
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```sql
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SELECT
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arrow_typeof(time) AS time,
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arrow_typeof(room) AS room,
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arrow_typeof(temp) AS temp,
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arrow_typeof(co) AS co
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FROM home
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LIMIT 1
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```
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| time | room | temp | co |
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| :-------------------------- | :---------------------- | :------ | :---- |
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| Timestamp(Nanosecond, None) | Dictionary(Int32, Utf8) | Float64 | Int64 |
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{{% /expand %}}
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{{< /expand-wrapper >}}
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## get_field
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Returns a field from a map or a struct with the specified key.
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> [!Note]
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> Typically, `get_field` is indirectly invoked via field access syntax such as
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> `my_struct['field_name']` which results in the call:
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> `get_field(my_struct, 'field_name')`.
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```sql
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get_field(collection, field)
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```
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### Arguments
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- **collection**: The map or struct to retrieve a field from.
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- **field**: The name of field the field to retrieve from the map or struct.
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Must evaluate to a string.
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{{< expand-wrapper >}}
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{{% expand "View `get_field` example with a struct column" %}}
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```sql
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SELECT
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get_field(influxdb_struct, 'version') AS influxdb_version
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FROM
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(VALUES (struct('influxdb' AS product, 'v1' AS version)),
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(struct('influxdb' AS product, 'v2' AS version)),
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(struct('influxdb' AS product, 'v3' AS version))
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) AS data(influxdb_struct)
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```
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| influxdb_version |
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| :--------------- |
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| v1 |
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| v2 |
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| v3 |
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{{% /expand %}}
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{{% expand "View `get_field` example with a map column" %}}
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```sql
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SELECT
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get_field(influxdb_map, 'version') AS influxdb_version
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FROM
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(VALUES (map {'product': 'influxdb', 'version': 'v1'}),
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(map {'product': 'influxdb', 'version': 'v2'}),
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(map {'product': 'influxdb', 'version': 'v3'})
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) AS data(influxdb_map)
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```
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| influxdb_version |
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| :--------------- |
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| v1 |
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| v2 |
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| v3 |
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{{% /expand %}}
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{{< /expand-wrapper >}}
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## interpolate
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Fills null values in a specified aggregated column by interpolating values
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from existing values.
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Must be used with [`date_bin_gapfill`](/influxdb/version/reference/sql/functions/time-and-date/#date_bin_gapfill).
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```sql
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interpolate(aggregate_expression)
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```
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### Arguments
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- **aggregate_expression**: Aggregate operation on a specified expression.
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The operation can use any [aggregate function](/influxdb/version/reference/sql/functions/aggregate/).
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The expression can be a constant, column, or function, and any combination of
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arithmetic operators supported by the aggregate function.
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##### Related functions
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[date_bin_gapfill](/influxdb/version/reference/sql/functions/time-and-date/#date_bin_gapfill),
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[locf](#locf)
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{{< expand-wrapper >}}
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{{% expand "View `interpolate` query example" %}}
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_The following example uses the sample data set provided in the
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[Get started with InfluxDB tutorial](/influxdb/version/get-started/write/#construct-line-protocol)._
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{{% influxdb/custom-timestamps %}}
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```sql
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SELECT
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date_bin_gapfill(INTERVAL '30 minutes', time) as _time,
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room,
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interpolate(avg(temp))
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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 <= '2022-01-01T10:00:00Z'
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GROUP BY _time, room
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```
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| _time | room | AVG(home.temp) |
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| :------------------- | :---------- | -------------: |
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| 2022-01-01T08:00:00Z | Kitchen | 21 |
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| 2022-01-01T08:30:00Z | Kitchen | 22 |
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| 2022-01-01T09:00:00Z | Kitchen | 23 |
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| 2022-01-01T09:30:00Z | Kitchen | 22.85 |
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| 2022-01-01T10:00:00Z | Kitchen | 22.7 |
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| 2022-01-01T08:00:00Z | Living Room | 21.1 |
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| 2022-01-01T08:30:00Z | Living Room | 21.25 |
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| 2022-01-01T09:00:00Z | Living Room | 21.4 |
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| 2022-01-01T09:30:00Z | Living Room | 21.6 |
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| 2022-01-01T10:00:00Z | Living Room | 21.8 |
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{{% /influxdb/custom-timestamps %}}
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{{% /expand %}}
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{{< /expand-wrapper >}}
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## locf
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Fills null values in a specified aggregated column by carrying the last observed
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value forward.
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Must be used with [`date_bin_gapfill`](/influxdb/version/reference/sql/functions/time-and-date/#date_bin_gapfill).
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_LOCF is an initialism of "last observation carried forward."_
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```sql
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locf(aggregate_expression)
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```
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### Arguments
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- **aggregate_expression**: Aggregate operation on a specified expression.
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The operation can use any [aggregate function](/influxdb/version/reference/sql/functions/aggregate/).
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The expression can be a constant, column, or function, and any combination of
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arithmetic operators supported by the aggregate function.
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##### Related functions
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[date_bin_gapfill](/influxdb/version/reference/sql/functions/time-and-date/#date_bin_gapfill),
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[interpolate](#interpolate)
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{{< expand-wrapper >}}
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{{% expand "View `locf` query example" %}}
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_The following example uses the sample data set provided in the
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[Get started with InfluxDB tutorial](/influxdb/version/get-started/write/#construct-line-protocol)._
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{{% influxdb/custom-timestamps %}}
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```sql
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SELECT
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date_bin_gapfill(INTERVAL '30 minutes', time) as _time,
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room,
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locf(avg(temp))
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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 <= '2022-01-01T10:00:00Z'
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GROUP BY _time, room
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```
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| _time | room | AVG(home.temp) |
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| :------------------- | :---------- | -------------: |
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| 2022-01-01T08:00:00Z | Kitchen | 21 |
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| 2022-01-01T08:30:00Z | Kitchen | 21 |
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| 2022-01-01T09:00:00Z | Kitchen | 23 |
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| 2022-01-01T09:30:00Z | Kitchen | 23 |
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| 2022-01-01T10:00:00Z | Kitchen | 22.7 |
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| 2022-01-01T08:00:00Z | Living Room | 21.1 |
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| 2022-01-01T08:30:00Z | Living Room | 21.1 |
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| 2022-01-01T09:00:00Z | Living Room | 21.4 |
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| 2022-01-01T09:30:00Z | Living Room | 21.4 |
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| 2022-01-01T10:00:00Z | Living Room | 21.8 |
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{{% /influxdb/custom-timestamps %}}
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{{% /expand %}}
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{{< /expand-wrapper >}}
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## version
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Returns the version of DataFusion.
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```sql
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version()
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```
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