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https://issues.apache.org/jira/browse/CALCITE-4597?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17406689#comment-17406689
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Xurenhe edited comment on CALCITE-4597 at 10/16/21, 12:44 PM:
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Hi [~julianhyde]
How is this issue going?
Is this option belong to the output field of current relnode?
Current relnode didn't know whether its output be used by its parent.
Should this option is applied for relnode's inputs, which input's field isn't
used by current relnode?
was (Author: wojustme):
Hi [~julianhyde]
How is this issue going?
Could you assign this issue to me, If it hasn't started yet.
I'm working the associated
issue([CALCITE-4743|https://issues.apache.org/jira/browse/CALCITE-4743])
> Allow RelNodes to have an empty row type (zero fields)
> ------------------------------------------------------
>
> Key: CALCITE-4597
> URL: https://issues.apache.org/jira/browse/CALCITE-4597
> Project: Calcite
> Issue Type: Bug
> Reporter: Julian Hyde
> Priority: Major
>
> Add an option, {{EmptyRowTypePolicy}}, to allow creation of {{RelNode}}s
> whose row type is empty. That is, contains zero fields.
> There are three values:
> * {{FORBIDDEN}} - Calcite prevents empty row type. (For example, planner and
> {{RelBuilder}} throw if they see one.) Rules must not produce empty row
> types. Rules can assume that they will not encounter empty row types.
> * {{DISCOURAGED}} - Empty row types are discouraged. (Planner and
> {{RelBuilder}} will not throw if they see one.) Rules must not fail if they
> encounter an empty row type. Rules should not produce empty row types (with
> reasonable exceptions, such as if the input has an empty row type).
> * {{ALLOWED}} - Empty row types are OK. All rules should handle {{RelNode}}s
> with empty row types, and it's OK if they generate {{RelNode}}s with empty
> row types.
> The current policy is effectively {{DISCOURAGED}}. We try not to create empty
> RelNodes, but we don't check, and they crop up occasionally.
> After this change, and for a few releases, the policy will be {{DISCOURAGED}}
> by default, but we will run tests in all three modes. All rules must run in
> all modes.
> At some point in the future, we will change the default policy to
> {{ALLOWED}}. All rules must continue to run in all modes.
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