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https://issues.apache.org/jira/browse/IMPALA-5821?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16542230#comment-16542230
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Tim Armstrong commented on IMPALA-5821:
---------------------------------------
Talked with Greg. The idea is to solve a bigger class of problems by printing
explicit casts in explain plans with level >= EXTENDED wherever it's currently
ambiguous:
* Where an implicit cast is inserted by the frontend
* With numeric types where literals of different types may be printed in the
same way
* Null literals?
This makes it easier to understand exactly what query execution will do when
looking at a profile. The advantage of using the cast syntax is that the output
will still be a valid expression.
> Distinguish numeric types and show implicit cast in EXTENDED explain plans
> --------------------------------------------------------------------------
>
> Key: IMPALA-5821
> URL: https://issues.apache.org/jira/browse/IMPALA-5821
> Project: IMPALA
> Issue Type: Improvement
> Components: Frontend
> Affects Versions: Impala 2.8.0
> Reporter: Matthew Jacobs
> Priority: Minor
> Labels: supportability, usability
>
> In this plan, it wasn't clear that the constant in the predicate was being
> evaluated to a double. Then the lhs required an implicit cast, and the
> predicate couldn't be pushed to Kudu:
> {code}
> [localhost:21000] > explain select * from functional_kudu.alltypestiny where
> bigint_col < 1000 / 100;
> Query: explain select * from functional_kudu.alltypestiny where bigint_col <
> 1000 / 100
> +---------------------------------------------+
> | Explain String |
> +---------------------------------------------+
> | Per-Host Resource Reservation: Memory=0B |
> | Per-Host Resource Estimates: Memory=10.00MB |
> | Codegen disabled by planner |
> | |
> | PLAN-ROOT SINK |
> | | |
> | 00:SCAN KUDU [functional_kudu.alltypestiny] |
> | predicates: bigint_col < 10 |
> +---------------------------------------------+
> {code}
> We should make it more clear by printing it in a way that makes it clear that
> it's being interpreted as a DOUBLE, e.g. by wrapping in a cast.
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