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SQL selector functions Selector functions Select data with SQL selector functions.
influxdb_cloud_iox
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Selectors sql-functions
220

SQL selector functions are designed to work with time series data. They behave similarly to aggregate functions in that they take a collection of data and return a single value. However, selectors are unique in that they return a struct that contains a time value in addition to the computed value.

How do selector functions work?

Each selector function returns a Rust struct (similar to a JSON object) representing a single time and value from the specified column in the each group. What time and value get returned depend on the logic in the selector function. For example, selector_first returns the value of specified column in the first row of the group. selector_max returns the maximum value of the specified column in the group.

Selector struct schema

The struct returned from a selector function has two properties:

  • time: time value in the selected row
  • value: value of the specified column in the selected row
{time: 2023-01-01T00:00:00Z, value: 72.1}

Selector functions in use

In your SELECT statement, execute a selector function and use bracket notation to reference properties of the returned struct to populate the column value:

SELECT
  selector_first(temp, time)['time'] AS time,
  selector_first(temp, time)['value'] AS temp,
  room
FROM home
GROUP BY room

Selector functions

selector_min

selector_min() function returns the smallest value of a selected column and a timestamp.

Arguments:
  • value: Column to operate on or a literal value.
  • timestamp: Time column or timestamp literal.
selector_min(<value>, <timestamp>)

{{< expand-wrapper >}} {{% expand "View selector_min query example" %}}

SELECT 
  selector_min(water_level, time)['time'] AS time,
  selector_min(water_level, time)['value'] AS water_level
FROM h2o_feet
time water_level
2019-08-28T14:30:00Z -0.61

{{% /expand %}} {{< /expand-wrapper >}}

selector_max

selector_max() function returns the smallest value of a selected column and a timestamp.

Arguments:
  • value: Column to operate on or a literal value.
  • timestamp: Time column or timestamp literal.
selector_max(<value>, <timestamp>)

{{< expand-wrapper >}} {{% expand "View selector_max query example" %}}

SELECT 
  selector_max(water_level, time)['time'] AS time,
  selector_max(water_level, time)['value'] AS water_level
FROM h2o_feet
time water_level
2019-08-28T07:24:00Z 9.964

{{% /expand %}} {{< /expand-wrapper >}}

selector_first

selector_first() returns the first value ordered by time ascending.

Arguments:
  • value: Column to operate on or a literal value.
  • timestamp: Time column or timestamp literal.
selector_first(<value>, <timestamp>)

{{< expand-wrapper >}} {{% expand "View selector_first query example" %}}

SELECT 
  selector_first(water_level, time)['time'] AS time,
  selector_first(water_level, time)['value'] AS water_level
FROM h2o_feet
time water_level
2019-08-28T07:24:00Z 9.964

{{% /expand %}} {{< /expand-wrapper >}}

selector_last

selector_last() returns the last value ordered by time ascending.

Arguments:
  • value: Column to operate on or a value literal.
  • timestamp: Time column or timestamp literal.
selector_last(<value>, <timestamp>)

{{< expand-wrapper >}} {{% expand "View selector_last query example" %}}

SELECT 
  selector_last(water_level, time)['time'] AS time,
  selector_last(water_level, time)['value'] AS water_level
FROM h2o_feet
time water_level
2019-09-17T21:42:00Z 4.938

{{% /expand %}} {{< /expand-wrapper >}}