[jira] [Created] (IMPALA-8285) In DESCRIBE output, display base table and column names

["Paul Rogers (JIRA)" <ji...@apache.org>]

Paul Rogers created IMPALA-8285:
-----------------------------------

             Summary: In DESCRIBE output, display base table and column names
                 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


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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