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From "Vineet Garg (JIRA)" <>
Subject [jira] [Commented] (HIVE-19770) Support for CBO for queries with multiple same columns in select
Date Fri, 20 Jul 2018 20:53:00 GMT


Vineet Garg commented on HIVE-19770:

Earlier patch removed the same column restriction from CBO path and added ambiguity check
(same as non-cbo path). But it turns out that ambiguity check is too restrictive e.g. queries
like {code:sql} select count(*) from (select key, key from src) subq {code} is not allowed
with this check. 
There are also queries which were successfully planned by CBO but now with this check are
not allowed e.g. {code:sql} select count(*) from (select t1.key, t2.key from src t1 inner
join src t2 on t1.key=t2.key)subq {code}
Therefore I have removed the ambiguity check for now and opened HIVE-20215 for fix this. Fixing
this will require checking ambiguity during column reference instead of generating column
list for select.

> Support for CBO for queries with multiple same columns in select
> ----------------------------------------------------------------
>                 Key: HIVE-19770
>                 URL:
>             Project: Hive
>          Issue Type: Improvement
>            Reporter: Vineet Garg
>            Assignee: Vineet Garg
>            Priority: Major
>         Attachments: HIVE-19770.1.patch, HIVE-19770.2.patch, HIVE-19770.3.patch, HIVE-19770.4.patch,
HIVE-19770.5.patch, HIVE-19770.6.patch
> Currently queries such as {code:sql} select a,a from t1 where b > 10 {code} are not
supported for CBO. 

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