[jira] [Commented] (CALCITE-5469) Implement BigQuery DATETIME_ADD/DATETIME_DIFF

["Julian Hyde (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CALCITE-5469?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17693531#comment-17693531 ] 

Julian Hyde commented on CALCITE-5469:
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It is difficult to discern the rule for whether date-time functions should truncate to the unit before they subtract. By experimentation, the rule seems to be:
 * The standard {{TIMESTAMPDIFF}} function does not truncate before subtraction;
 * BigQuery functions do not truncate before subtraction when applied to time units (e.g. {{HOUR}});
 * BigQuery functions ({{TIMESTAMP_DIFF}}, {{DATETIME_DIFF}}, {{DATE_DIFF}}) truncate before subtraction when applied to date units (e.g. {{DAY}}, {{WEEK}}, {{ISOWEEK}}, {{WEEK(WEDNESDAY)}}, {{SQL_TSI_YEAR}}, {{CENTURY}}).

> Implement BigQuery DATETIME_ADD/DATETIME_DIFF
> ---------------------------------------------
>
>                 Key: CALCITE-5469
>                 URL: https://issues.apache.org/jira/browse/CALCITE-5469
>             Project: Calcite
>          Issue Type: Sub-task
>            Reporter: Tanner Clary
>            Assignee: Tanner Clary
>            Priority: Major
>              Labels: pull-request-available
>          Time Spent: 2.5h
>  Remaining Estimate: 0h
>
> Add support for BigQuery's {{DATETIME_ADD/DATETIME_DIFF}} functions.
> {{DATETIME_ADD(datetime, interval)}} can accept a timestamp (or a datetime, which is an alias for timestamp) for its first argument and an interval for its second. The output is the datetime that occurs {{interval}} after the provided {{datetime}}.
> {{DATETIME_DIFF(datetime, datetime2, timeUnit)}} returns the whole number of {{timeUnit}} between {{datetime}} and {{datetime2}}, with the result being negative if {{datetime}} occurs before {{datetime2}}
> Examples:
> {{DATETIME_ADD(TIMESTAMP '2008-12-25 15:30:00', INTERVAL 5 MINUTE)}} would return: '2008-12-25 15:35:00'.
> {{DATETIME_DIFF(DATETIME '2008-12-25 15:30:00', DATETIME '2008-12-26 15:30:00', DAY)}} would return: -1.



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