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https://issues.apache.org/jira/browse/IMPALA-8285?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Paul Rogers updated IMPALA-8285:
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Summary: Display base table and column names in DESCRIBE expressions (was:
In DESCRIBE output, display base table and column names)
> Display base table and column names in DESCRIBE expressions
> -----------------------------------------------------------
>
> Key: IMPALA-8285
> URL: https://issues.apache.org/jira/browse/IMPALA-8285
> Project: IMPALA
> Issue Type: Improvement
> Components: Frontend
> Affects Versions: Impala 3.1.0
> Reporter: Paul Rogers
> Priority: Minor
>
> When a query has aliases or views, the DESCRIBE predicates often refer to
> these internal names, which is ambiguous. Instead, refer to base table and
> column names.
> Example PlannerTest case with a pathological use case in which the alias "a"
> is used multiple times.
> {noformat}
> select
> akey, bkey, ckey
> from
> (select a.c_custkey akey from tpch.customer a where a.c_nationkey = 10) a,
> (select a.c_custkey bkey from tpch.customer a where a.c_name < "fred") b,
> (select a.c_custkey ckey from tpch.customer a) c
> where akey = b.bkey
> and bkey = c.ckey
> # ==> a.c_custkey = c.c_custkey
> ---- PLAN
> PLAN-ROOT SINK
> |
> 04:HASH JOIN [INNER JOIN]
> | hash predicates: a.c_custkey = a.c_custkey
> |
> |--03:HASH JOIN [INNER JOIN]
> | | hash predicates: a.c_custkey = a.c_custkey
> | |
> | |--00:SCAN HDFS [tpch.customer a]
> | | predicates: a.c_nationkey = 10
> | |
> | 02:SCAN HDFS [tpch.customer a]
> | runtime filters: RF002 -> a.c_custkey
> |
> 01:SCAN HDFS [tpch.customer a]
> predicates: a.c_name < 'fred'
> {noformat}
> Notice that the root hash join predicate appears to be a tautology:
> {{a.c_custkey = a.c_custkey}}. This is actually {{b.c_custkey = a.c_custkey}}
> (using top-level aliases). Even this is unclear since "a" and "b" are also
> aliases. If we use table names we get {{customer.c_custkey =
> customer.c_custkey}} which is also ambiguous.
> Might be good to simply list tables using an unambiguous alias, or perhaps
> use comment to clarify: {{customer /\* b \*/.c_custkey = customer /\* a
> \*/.c_custkey}}.
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