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https://issues.apache.org/jira/browse/CALCITE-5476?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17676771#comment-17676771
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Julian Hyde commented on CALCITE-5476:
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Thanks for logging this with a good specification.
I expect that the implementation will be extremely similar to
{{TIMESTAMP_TRUNC}}. Possibly the only difference will be whether the internal
Java {{long}} value is interpreted as relative to a particular time zone. A
change of interpretation requires no code.
Any chance that this can be accomplished in the same PR as the other
{{DATETIME_}} functions? Fine-grained PRs, arriving in no particular order,
have been hell for this particular reviewer.
> Add DATETIME_TRUNC for BigQuery
> -------------------------------
>
> Key: CALCITE-5476
> URL: https://issues.apache.org/jira/browse/CALCITE-5476
> Project: Calcite
> Issue Type: Improvement
> Reporter: Oliver Lee
> Assignee: Oliver Lee
> Priority: Minor
>
> Adding in DATETIME_TRUNC() to the BigQuery library as described here:
> [https://cloud.google.com/bigquery/docs/reference/standard-sql/datetime_functions#datetime_trunc]
> Truncates a {{DATETIME}} value to the granularity of {{{}date_time_part{}}}.
> The {{DATETIME}} value is always rounded to the beginning of
> {{{}date_time_part{}}}, which can be one of the following:
> * {{{}MICROSECOND{}}}: If used, nothing is truncated from the value.
> * {{{}MILLISECOND{}}}: The nearest lessor or equal millisecond.
> * {{{}SECOND{}}}: The nearest lessor or equal second.
> * {{{}MINUTE{}}}: The nearest lessor or equal minute.
> * {{{}HOUR{}}}: The nearest lessor or equal hour.
> * {{{}DAY{}}}: The day in the Gregorian calendar year that contains the
> {{DATETIME}} value.
> * {{{}WEEK{}}}: The first day of the week in the week that contains the
> {{DATETIME}} value. Weeks begin on Sundays. {{WEEK}} is equivalent to
> {{{}WEEK(SUNDAY){}}}.
> * {{{}WEEK(WEEKDAY){}}}: The first day of the week in the week that contains
> the {{DATETIME}} value. Weeks begin on {{{}WEEKDAY{}}}. {{WEEKDAY}} must be
> one of the following: {{{}SUNDAY{}}}, {{{}MONDAY{}}}, {{{}TUESDAY{}}},
> {{{}WEDNESDAY{}}}, {{{}THURSDAY{}}}, {{{}FRIDAY{}}}, or {{{}SATURDAY{}}}.
> * {{{}ISOWEEK{}}}: The first day of the [ISO 8601
> week|https://en.wikipedia.org/wiki/ISO_week_date] in the ISO week that
> contains the {{DATETIME}} value. The ISO week begins on Monday. The first ISO
> week of each ISO year contains the first Thursday of the corresponding
> Gregorian calendar year.
> * {{{}MONTH{}}}: The first day of the month in the month that contains the
> {{DATETIME}} value.
> * {{{}QUARTER{}}}: The first day of the quarter in the quarter that contains
> the {{DATETIME}} value.
> * {{{}YEAR{}}}: The first day of the year in the year that contains the
> {{DATETIME}} value.
> * {{{}ISOYEAR{}}}: The first day of the [ISO
> 8601|https://en.wikipedia.org/wiki/ISO_8601] week-numbering year in the ISO
> year that contains the {{DATETIME}} value. The ISO year is the Monday of the
> first week whose Thursday belongs to the corresponding Gregorian calendar
> year.
>
>
> {{SELECT DATETIME_TRUNC(DATETIME "2008-12-25 15:30:00", DAY) ->
> 2008-12-25T00:00:00}}
> {{}}
> {{}}
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