Selectors

Use selector functions to assess, select, and return values in your data. Selector functions return one or more rows with the selected values from each InfluxQL group.

Examples use the sample data set provided in the Get started with InfluxDB tutorial.

• BOTTOM()
• FIRST()
• LAST()
• MAX()
• MIN()
• PERCENTILE()
• TOP()
• Notable behaviors of selector functions

[!Important]

Missing InfluxQL functions

Some InfluxQL functions are in the process of being rearchitected to work with the InfluxDB 3 storage engine. If a function you need is not here, check the InfluxQL feature support page for more information.

BOTTOM()

Returns the smallest N field values. BOTTOM() supports int64 and float64 field value data types.

BOTTOM(field_expression[, tag_expression_1[, ..., tag_expression_n]], N)

[!Note] Note: BOTTOM() returns the field value with the earliest timestamp if there's a tie between two or more values for the smallest value.

Arguments

• field_expression: Expression to identify the field to operate on. Can be a field key or constant.
• tag_expression: Expression to identify a tag key to segment by. Can be a tag key or constant. Comma-delimit multiple tags.
• N: Number of results to return from each InfluxQL group or specified tag segment.

Notable behaviors

• BOTTOM() maintains original timestamps when grouping by time.
• BOTTOM() may return fewer points than expected.

Examples

{{< expand-wrapper >}} {{% expand "Select the bottom three values of a field" %}}

SELECT BOTTOM(temp, 3) FROM home

{{% influxql/table-meta %}} name: home {{% /influxql/table-meta %}} {{% influxdb/custom-timestamps %}}

{{% /influxdb/custom-timestamps %}} {{% /expand %}}

{{% expand "Select the bottom field value for two unique tag values" %}}

SELECT BOTTOM(temp, room, 2) FROM home

{{% influxql/table-meta %}} name: home {{% /influxql/table-meta %}} {{% influxdb/custom-timestamps %}}

{{% /influxdb/custom-timestamps %}} {{% /expand %}}

{{% expand "Select the bottom three field values and the tag value associated with each" %}}

SELECT BOTTOM(temp, 3), room FROM home

{{% influxql/table-meta %}} name: home {{% /influxql/table-meta %}} {{% influxdb/custom-timestamps %}}

{{% /influxdb/custom-timestamps %}} {{% /expand %}}

{{% expand "Select the bottom field values for unique tag values and within time windows (grouped by time)" %}}

{{% influxdb/custom-timestamps %}}

SELECT
  BOTTOM(temp, room, 2)
FROM home
WHERE
  time >= '2022-01-01T08:00:00Z'
  AND time <= '2022-01-01T12:00:00Z'
GROUP BY time(2h)

{{% influxql/table-meta %}} name: home {{% /influxql/table-meta %}}

{{% /influxdb/custom-timestamps %}}

Notice that when grouping by time, BOTTOM() maintains the point's original timestamp.

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

FIRST()

Returns the field value with the oldest timestamp.

FIRST(field_expression)

Arguments

• field_expression: Expression to identify one or more fields to operate on. Can be a field key, constant, regular expression, or wildcard (*). Supports all field data types.

Notable behaviors

• FIRST() overrides original timestamps when grouping by time

Examples

{{< expand-wrapper >}} {{% expand "Select the first value for a field" %}}

SELECT FIRST(temp) FROM home

{{% influxql/table-meta %}} name: home {{% /influxql/table-meta %}}

{{% influxdb/custom-timestamps %}}

{{% /influxdb/custom-timestamps %}}

{{% /expand %}}

{{% expand "Select the first value from each field" %}}

SELECT FIRST(*) FROM home

{{% influxql/table-meta %}} name: home {{% /influxql/table-meta %}}

{{% /expand %}}

{{% expand "Select the first value from field keys that match a regular expression" %}}

SELECT FIRST(/^[th]/) FROM home

{{% influxql/table-meta %}} name: home {{% /influxql/table-meta %}}

{{% /expand %}}

{{% expand "Select the first value from a field within time windows (grouped by time)" %}}

{{% influxdb/custom-timestamps %}}

SELECT
  FIRST(temp)
FROM home 
WHERE
  room = 'Kitchen'
  AND time >= '2022-01-01T08:00:00Z'
  AND time <= '2022-01-01T20:00:00Z'
GROUP BY time(6h)

{{% influxql/table-meta %}} name: home {{% /influxql/table-meta %}}

{{% /influxdb/custom-timestamps %}}

Notice that when grouping by time, FIRST() overrides the point's original timestamp.

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

LAST()

Returns the field value with the most recent timestamp.

LAST(field_expression)

Arguments

• field_expression: Expression to identify one or more fields to operate on. Can be a field key, constant, regular expression, or wildcard (*). Supports all field data types.

Notable behaviors

• LAST() overrides original timestamps when grouping by time

Examples

{{< expand-wrapper >}}

{{% expand "Select the last value for a field" %}}

SELECT LAST(temp) FROM home

{{% influxql/table-meta %}} name: home {{% /influxql/table-meta %}}

{{% influxdb/custom-timestamps %}}

{{% /influxdb/custom-timestamps %}}

{{% /expand %}}

{{% expand "Select the last value from each field" %}}

SELECT LAST(*) FROM home

{{% influxql/table-meta %}} name: home {{% /influxql/table-meta %}}

{{% /expand %}}

{{% expand "Select the last value from field keys that match a regular expression" %}}

SELECT LAST(/^[th]/) FROM home

{{% influxql/table-meta %}} name: home {{% /influxql/table-meta %}}

{{% /expand %}}

{{% expand "Select the last value from a field within time windows (grouped by time)" %}}

{{% influxdb/custom-timestamps %}}

SELECT
  LAST(temp)
FROM home 
WHERE
  room = 'Kitchen'
  AND time >= '2022-01-01T08:00:00Z'
  AND time <= '2022-01-01T20:00:00Z'
GROUP BY time(6h)

{{% influxql/table-meta %}} name: home {{% /influxql/table-meta %}}

{{% /influxdb/custom-timestamps %}}

Notice that when grouping by time, LAST() overrides the point's original timestamp.

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

MAX()

Returns the greatest field value.

MAX(field_expression)

Arguments

• field_expression: Expression to identify one or more fields to operate on. Can be a field key, constant, regular expression, or wildcard (*). Supports numeric fields.

Notable behaviors

• MAX() overrides original timestamps when grouping by time.

Examples

{{< expand-wrapper >}}

{{% expand "Select the maximum value from a field" %}}

SELECT MAX(co) FROM home

{{% influxql/table-meta %}} name: home {{% /influxql/table-meta %}}

{{% influxdb/custom-timestamps %}}

{{% /influxdb/custom-timestamps %}}

{{% /expand %}}

{{% expand "Select the maximum value from each field" %}}

SELECT MAX(*) FROM home

{{% influxql/table-meta %}} name: home {{% /influxql/table-meta %}}

{{% /expand %}}

{{% expand "Select the maximum value from field keys that match a regular expression" %}}

SELECT MAX(/^[th]/) FROM home

{{% influxql/table-meta %}} name: home {{% /influxql/table-meta %}}

{{% /expand %}}

{{% expand "Select the maximum value from a field within time windows (grouped by time)" %}}

{{% influxdb/custom-timestamps %}}

SELECT
  MAX(temp)
FROM home
WHERE
  room = 'Kitchen'
  AND time >= '2022-01-01T08:00:00Z'
  AND time <= '2022-01-01T20:00:00Z'
GROUP BY time(6h)

{{% influxql/table-meta %}} name: home {{% /influxql/table-meta %}}

{{% /influxdb/custom-timestamps %}}

Notice that when grouping by time, MAX() overrides the point's original timestamp.

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

MIN()

Returns the lowest field value.

MIN(field_expression)

Arguments

• field_expression: Expression to identify one or more fields to operate on. Can be a field key, constant, regular expression, or wildcard (*). Supports numeric fields.

Notable behaviors

• MIN() overrides original timestamps when grouping by time.

Examples

{{< expand-wrapper >}}

{{% expand "Select the minimum value from a field" %}}

SELECT MIN(temp) FROM home

{{% influxql/table-meta %}} name: home {{% /influxql/table-meta %}}

{{% influxdb/custom-timestamps %}}

{{% /influxdb/custom-timestamps %}}

{{% /expand %}}

{{% expand "Select the minimum value from each field" %}}

SELECT MIN(*) FROM home

{{% influxql/table-meta %}} name: home {{% /influxql/table-meta %}}

{{% /expand %}}

{{% expand "Select the minimum value from field keys that match a regular expression" %}}

SELECT MIN(/^[th]/) FROM home

{{% influxql/table-meta %}} name: home {{% /influxql/table-meta %}}

{{% /expand %}}

{{% expand "Select the minimum value from a field within time windows (grouped by time)" %}}

{{% influxdb/custom-timestamps %}}

SELECT
  MIN(temp)
FROM home
WHERE
  room = 'Kitchen'
  AND time >= '2022-01-01T08:00:00Z'
  AND time <= '2022-01-01T20:00:00Z'
GROUP BY time(6h)

{{% influxql/table-meta %}} name: home {{% /influxql/table-meta %}}

{{% /influxdb/custom-timestamps %}}

Notice that when grouping by time, MIN() overrides the point's original timestamp.

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

PERCENTILE()

Returns the Nth percentile field value.

PERCENTILE(field_expression, N)

Arguments

• field_expression: Expression to identify one or more fields to operate on. Can be a field key, constant, regular expression, or wildcard (*). Supports numeric fields.
• N: Percentile to return. Must be an integer or float value greater than 0 and less than or equal to 100.

Notable behaviors

• PERCENTILE() overrides original timestamps when grouping by time.
• PERCENTILE(example_field, 100) is equivalent to MAX(example_field).
• PERCENTILE(example_field, 50) is nearly equivalent to MEDIAN(example_field), except MEDIAN() returns the average of the two middle values if the field contains an even number of values.
• PERCENTILE(example_field, 0) returns null.

Examples

{{< expand-wrapper >}}

{{% expand "Select the 50th percentile value from a field" %}}

SELECT PERCENTILE(temp, 50) FROM home

{{% influxql/table-meta %}} name: home {{% /influxql/table-meta %}}

{{% influxdb/custom-timestamps %}}

{{% /influxdb/custom-timestamps %}}

{{% /expand %}}

{{% expand "Select the 50th percentile value from each field" %}}

SELECT PERCENTILE(*, 50) FROM home

{{% influxql/table-meta %}} name: home {{% /influxql/table-meta %}}

{{% /expand %}}

{{% expand "Select the 50th percentile value from field keys that match a regular expression" %}}

SELECT PERCENTILE(/^[th]/, 50) FROM home

{{% influxql/table-meta %}} name: home {{% /influxql/table-meta %}}

{{% /expand %}}

{{% expand "Select the 50th percentile value from a field within time windows (grouped by time)" %}}

{{% influxdb/custom-timestamps %}}

SELECT
  PERCENTILE(temp, 50)
FROM home
WHERE
  room = 'Kitchen'
  AND time >= '2022-01-01T08:00:00Z'
  AND time <= '2022-01-01T20:00:00Z'
GROUP BY time(6h)

{{% influxql/table-meta %}} name: home {{% /influxql/table-meta %}}

{{% /influxdb/custom-timestamps %}}

Notice that when grouping by time, PERCENTILE() overrides the point's original timestamp.

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

TOP()

Returns the greatest N field values. TOP() supports int64 and float64 field value data types.

TOP(field_expression[, tag_expression_1[, ..., tag_expression_n]], N)

[!Note] Note: TOP() returns the field value with the earliest timestamp if there's a tie between two or more values for the greatest value.

Arguments

• field_expression: Expression to identify the field to operate on. Can be a field key or constant.
• tag_expression: Expression to identify a tag key to segment by. Can be a tag key or constant. Comma-delimit multiple tags.
• N: Number of results to return from each InfluxQL group or specified tag segment.

Notable behaviors

• TOP() maintains original timestamps when grouping by time.
• TOP() may return fewer points than expected.

Examples

{{< expand-wrapper >}} {{% expand "Select the top three values of a field" %}}

SELECT TOP(temp, 3) FROM home

{{% influxql/table-meta %}} name: home {{% /influxql/table-meta %}} {{% influxdb/custom-timestamps %}}

{{% /influxdb/custom-timestamps %}} {{% /expand %}}

{{% expand "Select the top field value for two unique tag values" %}}

SELECT TOP(temp, room, 2) FROM home

{{% influxql/table-meta %}} name: home {{% /influxql/table-meta %}} {{% influxdb/custom-timestamps %}}

{{% /influxdb/custom-timestamps %}} {{% /expand %}}

{{% expand "Select the top three field values and the tag value associated with each" %}}

SELECT TOP(temp, 3), room FROM home

{{% influxql/table-meta %}} name: home {{% /influxql/table-meta %}} {{% influxdb/custom-timestamps %}}

{{% /influxdb/custom-timestamps %}} {{% /expand %}}

{{% expand "Select the top field values for unique tag values and within time windows (grouped by time)" %}}

{{% influxdb/custom-timestamps %}}

SELECT
  TOP(temp, room, 2)
FROM home
WHERE
  time >= '2022-01-01T08:00:00Z'
  AND time <= '2022-01-01T12:00:00Z'
GROUP BY time(2h)

{{% influxql/table-meta %}} name: home {{% /influxql/table-meta %}}

{{% /influxdb/custom-timestamps %}}

Notice that when grouping by time, TOP() maintains the point's original timestamp.

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

Notable behaviors of selector functions

• Timestamps when grouping by time
• Selector functions may return fewer points than expected

Timestamps when grouping by time

When using selector functions with a GROUP BY time() clause, most selector functions return the timestamp of the starting boundary for each time interval. However functions with an N argument that specifies the number of results to return per group maintain the original timestamp of each returned point.

{{< flex >}} {{% flex-content %}}

Return the start time of each time interval

• FIRST()
• LAST()
• MAX()
• MIN()
• PERCENTILE()

{{% /flex-content %}} {{% flex-content %}}

Maintain the original timestamp

• BOTTOM()
• TOP()

{{% /flex-content %}} {{< /flex >}}

Selector functions may return fewer points than expected

Queries that use the following selector functions with an N argument may return fewer points than expected.

• BOTTOM()
• TOP()

If the InfluxQL group or specified tag key contains X points or unique tag values and X is less than N, the function returns X results instead of N for each group or tag value.

{{< expand-wrapper >}} {{% expand "View example for FN(field_key, N)" %}}

The example below selects the bottom 5 temperatures from the Kitchen between {{% influxdb/custom-timestamps-span %}}2022-01-01T08:00:00Z{{% /influxdb/custom-timestamps-span %}} and {{% influxdb/custom-timestamps-span %}}2022-01-01T10:00:00Z{{% /influxdb/custom-timestamps-span %}}. There are only 3 points recorded for the Kitchen during the queried time range, so the query returns 3 points instead of 5.

{{% influxdb/custom-timestamps %}}

SELECT BOTTOM(temp, 5)
FROM home
WHERE
  time >= '2022-01-01T08:00:00Z'
  AND time <= '2022-01-01T10:00:00Z'
  AND room = 'Kitchen'

{{% /influxdb/custom-timestamps %}}

{{% /expand %}} {{% expand "View example for FN(field_key, tag_key, N)" %}}

The example below selects the top temperature from 3 unique values of the room tag. However, the room tag only has 2 unique values, so results only contain 2 values.

SELECT TOP(temp, room, 3) FROM home

{{% influxdb/custom-timestamps %}}

{{% /influxdb/custom-timestamps %}}

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