InfluxQL selector functions

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

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)

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

SELECT BOTTOM(temp, 3) FROM home

SELECT BOTTOM(temp, room, 2) FROM home

SELECT BOTTOM(temp, 3), room FROM home

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)

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

SELECT FIRST(temp) FROM home

SELECT FIRST(*) FROM home

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

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)

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

SELECT LAST(temp) FROM home

SELECT LAST(*) FROM home

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

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)

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

SELECT MAX(co) FROM home

SELECT MAX(*) FROM home

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

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)

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

SELECT MIN(temp) FROM home

SELECT MIN(*) FROM home

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

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)

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

SELECT PERCENTILE(temp, 50) FROM home

SELECT PERCENTILE(*, 50) FROM home

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

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)

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)

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

SELECT TOP(temp, 3) FROM home

SELECT TOP(temp, room, 2) FROM home

SELECT TOP(temp, 3), room FROM home

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)

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.

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.

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

SELECT TOP(temp, room, 3) FROM home