Documentation

SQL selector functions

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 an Arrow 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

Returns the smallest value of a selected column and a timestamp.

selector_min(expression, timestamp)
Arguments
  • expression: Expression to operate on. Can be a constant, column, or function, and any combination of string or arithmetic operators.
  • timestamp: Time expression. Can be a constant, column, or function.

View selector_min query example

selector_max

Returns the largest value of a selected column and a timestamp.

selector_max(expression, timestamp)
Arguments
  • expression: Expression to operate on. Can be a constant, column, or function, and any combination of string or arithmetic operators.
  • timestamp: Time expression. Can be a constant, column, or function.

View selector_max query example

selector_first

Returns the first value ordered by time ascending.

selector_first(expression, timestamp)
Arguments
  • expression: Expression to operate on. Can be a constant, column, or function, and any combination of string or arithmetic operators.
  • timestamp: Time expression. Can be a constant, column, or function.

View selector_first query example

selector_last

Returns the last value ordered by time ascending.

selector_last(expression, timestamp)
Arguments
  • expression: Expression to operate on. Can be a constant, column, or function, and any combination of string or arithmetic operators.
  • timestamp: Time expression. Can be a constant, column, or function.

View selector_last query example


Was this page helpful?

Thank you for your feedback!


The future of Flux

Flux is going into maintenance mode. You can continue using it as you currently are without any changes to your code.

Flux is going into maintenance mode and will not be supported in InfluxDB 3.0. This was a decision based on the broad demand for SQL and the continued growth and adoption of InfluxQL. We are continuing to support Flux for users in 1.x and 2.x so you can continue using it with no changes to your code. If you are interested in transitioning to InfluxDB 3.0 and want to future-proof your code, we suggest using InfluxQL.

For information about the future of Flux, see the following:

InfluxDB Cloud Serverless