Tanner Clary created CALCITE-5757:
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Summary: Incorrect return type for BigQuery TIMESTAMP functions
Key: CALCITE-5757
URL: https://issues.apache.org/jira/browse/CALCITE-5757
Project: Calcite
Issue Type: Bug
Reporter: Tanner Clary
Assignee: Tanner Clary
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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