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https://issues.apache.org/jira/browse/CALCITE-2470?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16624866#comment-16624866
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Julian Hyde commented on CALCITE-2470:
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I don't really want it to be easy to use - I don't think people should disable
merging projects, and I don't think people should sub-class RelBuilder to
override its behavior (PigRelBuilder overriding to extend its behavior is kind
of OK). But the Drill folks really wanted this to be configurable.
Are the problems with PigRelBuilder real or theoretical? I mean, is anyone who
actually wants to use PigRelBuilder hitting them?
> RelBuilder.project should combine expressions if underlying node is a Project
> -----------------------------------------------------------------------------
>
> Key: CALCITE-2470
> URL: https://issues.apache.org/jira/browse/CALCITE-2470
> Project: Calcite
> Issue Type: Bug
> Reporter: Julian Hyde
> Assignee: Julian Hyde
> Priority: Major
> Fix For: 1.18.0
>
>
> The {{RelBuilder.project}} method should combine expressions if underlying
> node is a {{Project}}.
> For example, if {{r}} is a {{RelBuilder}} and its stack initially contains
> {code:java}
> Project(Scan(T), a, b, a + b as c){code}
> and we call (in pseudo-code)
> {code:java}
> r.project(a + c as d){code}
> then the result should be
> {code:java}
> Project(Scan(T), a + (a + b) as d){code}
> Today the result is
> {code:java}
> Project(Project(Scan(T), a, a + b as c), a + c as d){code}
> In some circumstances the result will be larger (i.e. contain more
> {{RexNode}} instances) but much more frequently the result will be smaller
> and simpler.
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