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From Gergely Hajós (JIRA) <j...@apache.org>
Subject [jira] [Assigned] (HIVE-17342) Where condition with 1=0 should be treated similar to limit 0
Date Wed, 13 Sep 2017 11:31:00 GMT

     [ https://issues.apache.org/jira/browse/HIVE-17342?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Gergely Hajós reassigned HIVE-17342:
------------------------------------

    Assignee: Gergely Hajós

> Where condition with 1=0 should be treated similar to limit 0
> -------------------------------------------------------------
>
>                 Key: HIVE-17342
>                 URL: https://issues.apache.org/jira/browse/HIVE-17342
>             Project: Hive
>          Issue Type: Improvement
>            Reporter: Rajesh Balamohan
>            Assignee: Gergely Hajós
>            Priority: Minor
>
> In some cases, queries may get executed with where condition mentioning to "1=0" to get
schema. E.g 
> {noformat}
> SELECT * FROM (select avg(d_year) as  y from date_dim where d_year>1999) q WHERE 1=0
> {noformat}
> Currently hive executes the query; it would be good to consider this similar to "limit
0" which does not execute the query.
> {code}
> hive> explain SELECT * FROM (select avg(d_year) as  y from date_dim where d_year>1999)
q WHERE 1=0;
> OK
> Plan optimized by CBO.
> Vertex dependency in root stage
> Reducer 2 <- Map 1 (CUSTOM_SIMPLE_EDGE)
> Stage-0
>   Fetch Operator
>     limit:-1
>     Stage-1
>       Reducer 2 vectorized, llap
>       File Output Operator [FS_13]
>         Group By Operator [GBY_12] (rows=1 width=76)
>           Output:["_col0"],aggregations:["avg(VALUE._col0)"]
>         <-Map 1 [CUSTOM_SIMPLE_EDGE] vectorized, llap
>           PARTITION_ONLY_SHUFFLE [RS_11]
>             Group By Operator [GBY_10] (rows=1 width=76)
>               Output:["_col0"],aggregations:["avg(d_year)"]
>               Filter Operator [FIL_9] (rows=1 width=0)
>                 predicate:false
>                 TableScan [TS_0] (rows=1 width=0)
>                   default@date_dim,date_dim,Tbl:PARTIAL,Col:NONE,Output:["d_year"]
> {code}
> It does generate 0 splits, but does send a DAG plan to the AM and receive 0 rows as output.



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