[IMPALA-7953] EXPLAIN does not reliably show table aliases

• Type: Bug
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Affects Version/s: Impala 3.1.0
• Component/s: Frontend
• Epic Color: ghx-label-4
• Assignee: Unassigned
• Reporter: Paul Rogers
• Created: 10/Dec/18 22:23
• Updated: 10/Dec/18 22:23

Description

Consider one of the queries in PlannerTest.testJoins():

# test that on-clause predicates referring to multiple tuple ids
# get registered as eq join conjuncts
select t1.*
from (select * from functional.alltypestiny) t1
  join (select * from functional.alltypestiny) t2 on (t1.id = t2.id)
  join functional.alltypestiny t3 on (coalesce(t1.id, t2.id) = t3.id)
---- PLAN
PLAN-ROOT SINK
|
04:HASH JOIN [INNER JOIN]
|  hash predicates: coalesce(functional.alltypestiny.id, functional.alltypestiny.id) = t3.id
|  runtime filters: RF000 <- t3.id
|
|--02:SCAN HDFS [functional.alltypestiny t3]
|     partitions=4/4 files=4 size=460B
|
03:HASH JOIN [INNER JOIN]
|  hash predicates: functional.alltypestiny.id = functional.alltypestiny.id
|  runtime filters: RF002 <- functional.alltypestiny.id
|
|--01:SCAN HDFS [functional.alltypestiny]
|     partitions=4/4 files=4 size=460B
|     runtime filters: RF000 -> coalesce(functional.alltypestiny.id, functional.alltypestiny.id)
|
00:SCAN HDFS [functional.alltypestiny]
   partitions=4/4 files=4 size=460B
   runtime filters: RF000 -> coalesce(functional.alltypestiny.id, functional.alltypestiny.id), RF002 -> functional.alltypestiny.id

This query uses self-joins so the table name is not sufficient to explain the join decisions. Note that the 02 Scan shows the table alias, `t3`, for that table. But, the 00 and 01 scans do not. As a result, we can't readily tell which alias was placed where.

Expected that all scan nodes would show the table alias, if the user provided one in the SQL.