feat: Implement date_part scalar function

[devanbenz]

Implement date_part(part, expression)

Arguments

- part: Part of the date to return. The following date parts are supported:
   - year
    - quarter (emits value in inclusive range [1, 4] based on which quartile of the year the date is in)
    - month
    - week (week of the year)
    - day (day of the month)
    - hour
    - minute
    - second
    - millisecond
    - microsecond
    - nanosecond
    - dow (day of the week where Sunday is 0)
    - doy (day of the year)
    - epoch (seconds since Unix epoch)
    - isodow (day of the week where Monday is 0)
- expression: Time expression to operate on. Must be time VarRef

Example usage:

SELECT * FROM some_measurement
WHERE time >= now() - 10d AND time <= now() AND (date_part(time, dow) != 0 AND date_part(time, dow) != 6)

SELECT value, date_part('hour', time) FROM some_measurement

Please see #27001 (comment) for additional information on date_part limitations in 1.x.

[gwossum]

What is date_part_time? I don't see any tests for it.

[devanbenz]

It's used to create a reference to time since time is an auxiliary field https://github.com/influxdata/influxdb/pull/27005/files#diff-609a7e16be956ed6386e1a4a4efadf600b7d4de7dcfea27330dc692d1e901dc8R930-R944 I'm going to create some ValueMapper tests for this.

[devanbenz]

@gwossum I can add tests for this but it would likely require exporting

influxdb/query/select.go

Line 881 in 362217b

type valueMapper struct {

and testing it. We don't currently have any valueMapper specific tests. It's basically just a struct filled with maps so we would likely just be testing go's map functionality, which may not be worth the effort?

[davidby-influx]

Some changes from the first pass. Will review again after changes.

[davidby-influx]

In the spec, it says:

expression: Time expression to operate on. Can be a constant, column, or function.

Here it looks like you are prohibiting anything not the time column. Which is correct?

[devanbenz]

I need to modify our version of the spec. I think it should only operate on the time column. For v3 they can decide if they would like to add more features and allow it to work on constants.

[devanbenz]

I just changed the spec in the PR description to match: #27001 I recall we had a conversation yesterday during standup about the usefulness of constant timestamps. I verified that for other functions in influxdb 1.x (math functions predominately) we don't allow constants, so implementing a constant here would be non-trivial.

[devanbenz]

Testing with influx cli changes:

> SELECT count(*) FROM cpu GROUP BY date_part('year', time),date_part('month', time),host
name: cpu
tags: host=server01
group: month
time count_value year month
---- ----------- ---- -----
0    4                1
0    2                4
0    1                7

name: cpu
tags: host=server01
group: year
time count_value year month
---- ----------- ---- -----
0    7           2023

name: cpu
tags: host=server02
group: month
time count_value year month
---- ----------- ---- -----
0    2                1
0    2                2
0    2                5
0    2                8
0    1                10
0    1                11
0    1                12

name: cpu
tags: host=server02
group: year
time count_value year month
---- ----------- ---- -----
0    2           2023
0    9           2024

name: cpu
tags: host=server03
group: month
time count_value year month
---- ----------- ---- -----
0    1                1
0    1                6
0    5                9
0    1                12

name: cpu
tags: host=server03
group: year
time count_value year month
---- ----------- ---- -----
0    1           2024
0    7           2025

[Copilot]

Pull request overview

Adds InfluxQL support for a date_part(part, time) scalar function (including validation, evaluation, and query planning hooks) and extends query execution to support GROUP BY date_part(...) by threading date-part-derived grouping metadata through iterators and result emission.

Changes:

• Implement date_part parsing/validation, runtime evaluation (DatePartValuer), and date-part extraction helpers.
• Add iterator/planner plumbing to (a) evaluate date_part() in WHERE conditions using the point timestamp and (b) support GROUP BY date_part(...) via an extensible DimensionGrouper.
• Extend result/CLI structures to carry and display non-tag grouping metadata (grouping_keys) and add broad integration tests.

Reviewed changes

Copilot reviewed 21 out of 21 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tsdb/shard.go	Switch illegal "time" tag/field checks to use models.TimeBytes.
tsdb/field_validator.go	Switch illegal "time" field checks to use models.TimeBytes.
tsdb/engine/tsm1/iterator.gen.go.tmpl	Add timestamp mapping for condition eval and compute date-part aux values for grouping.
tsdb/engine/tsm1/iterator.gen.go	Generated iterator changes mirroring template updates (time mapping + date-part aux).
query/date_part.go	New: date_part core implementation (validation, extraction, valuer, grouper + encoding).
query/dimension_grouper.go	New: abstraction for non-tag/time grouping key resolution.
query/iterator.go	Extend IteratorOptions with date-part dimension support and cache NeedTimeRef.
query/select.go	Add date-part GROUP BY dimensions as output columns and adjust mapper handling for date_part.
query/iterator.gen.go.tmpl	Teach scanners/reducers about date-part grouping entries and time constant usage.
query/iterator.gen.go	Generated query iterator changes for grouping-key resolution and scan handling.
query/cursor.go	Add grouping_keys propagation via scanner cursor and enable date_part evaluation via timestamp injection.
query/emitter.go	Include grouping keys in row emission and header suppression behavior.
query/functions.go	Register date_part return type as Integer.
query/compile.go	Allow date_part() in dimensions and conditions; validate date_part calls.
query/compile_test.go	Add compile success/failure coverage for date_part.
query/date_part_test.go	New: unit tests for parsing/validation/valuer and date-part grouper round-trips.
models/time.go	Add models.TimeBytes/models.TimeString shared constants.
models/rows.go	Add GroupingKeys to API row model and incorporate it into series equality logic.
coordinator/statement_executor.go	Use models.TimeString for result column naming.
cmd/influx/cli/cli.go	Suppress headers only when grouping keys match; display grouping keys in formatted output.
tests/server_test.go	Large integration suite for date_part in WHERE/SELECT/GROUP BY/subqueries.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

Pull request overview

Copilot reviewed 21 out of 21 changed files in this pull request and generated 3 comments.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

Pull request overview

Copilot reviewed 21 out of 21 changed files in this pull request and generated 1 comment.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

This test explicitly encodes known-wrong behavior: SELECT COUNT(value), date_part('year', time) ... GROUP BY ... returns date_part=2023 for all groups (see note), even though the grouped year column is correct (2024/2025). This should be fixed in the implementation (e.g., rewrite date_part(...) in the SELECT list to reference the computed date_part dimension VarRef when it matches a GROUP BY date_part), and then the expected JSON should be updated to assert the correct per-group date_part value.