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https://issues.apache.org/jira/browse/CALCITE-5757?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Tanner Clary updated CALCITE-5757:
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Summary: Incorrect return type for BigQuery TRUNCfunctions (was: Incorrect
return type for BigQuery TIMESTAMP functions)
> Incorrect return type for BigQuery TRUNCfunctions
> -------------------------------------------------
>
> Key: CALCITE-5757
> URL: https://issues.apache.org/jira/browse/CALCITE-5757
> Project: Calcite
> Issue Type: Bug
> Reporter: Tanner Clary
> Assignee: Tanner Clary
> Priority: Major
>
> This is written in Calcite terms, a Calcite {{TIMESTAMP}} is a BigQuery
> {{DATETIME}} and a Calcite {{TIMESTAMP_LTZ}} is a BigQuery {{TIMESTAMP}}
> Some BigQuery operators, such as {{TIMESTAMP_TRUNC}}, currently have their
> return type set to {{TIMESTAMP_NULLABLE}}. This causes behavior which does
> not mirror BigQuery. {{TIMESTAMP_TRUNC}} can accept either a {{TIMESTAMP}} or
> a {{TIMESTAMP_LTZ}} and the return type should match the operand type (i.e.
> the return type should be ARG0}}.
> This can lead to discrepancies with queries like the following:
> {{SELECT CAST(TIMESTAMP_TRUNC([some TIMESTAMP_LTZ], MONTH) AS TIMESTAMP)}}
> because {{TIMESTAMP_TRUNC}} is currently implemented to return a
> {{TIMESTAMP}} the cast is deemed unnecessary and removed, when in reality the
> function should return a {{TIMESTAMP_LTZ}}, in which case the {{CAST}} is not
> redundant.
> The goal of this case is to adjust the return types of the BigQuery TIMESTAMP
> functions so that they correctly align with BigQuery behavior.
> [Relevant
> Docs|https://cloud.google.com/bigquery/docs/reference/standard-sql/timestamp_functions#timestamp_trunc]
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