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From "Carl Steinbach (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-3006) Skip execution of queries with always false WHERE clauses
Date Sun, 06 May 2012 01:41:47 GMT

    [ https://issues.apache.org/jira/browse/HIVE-3006?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13269100#comment-13269100
] 

Carl Steinbach commented on HIVE-3006:
--------------------------------------

Some clients (e.g. ODBC clients) execute queries with constant WHERE clauses that are always
false in order to generate a result set without incurring the expense of actually executing
the query. Unfortunately, this technique does not work with Hive:

{noformat}
hive> SELECT key FROM src WHERE false;
SELECT key FROM src WHERE false;
Total MapReduce jobs = 1
Launching Job 1 out of 1
Number of reduce tasks is set to 0 since there's no reduce operator
Execution log at: /tmp/carl/carl_20120505183939_4008b766-5637-4c5d-8cb0-22fb222ee228.log
Job running in-process (local Hadoop)
Hadoop job information for null: number of mappers: 0; number of reducers: 0
2012-05-05 18:39:15,923 null map = 100%,  reduce = 0%
Ended Job = job_local_0001
Execution completed successfully
Mapred Local Task Succeeded . Convert the Join into MapJoin
OK
Time taken: 3.664 seconds

hive> SELECT key FROM src WHERE 1=0;
SELECT key FROM src WHERE 1=0;
Total MapReduce jobs = 1
Launching Job 1 out of 1
Number of reduce tasks is set to 0 since there's no reduce operator
Execution log at: /tmp/carl/carl_20120505184040_074bd38d-2697-40e2-996a-91a46aaad71b.log
Job running in-process (local Hadoop)
Hadoop job information for null: number of mappers: 0; number of reducers: 0
2012-05-05 18:40:11,407 null map = 100%,  reduce = 0%
Ended Job = job_local_0001
Execution completed successfully
Mapred Local Task Succeeded . Convert the Join into MapJoin
OK
Time taken: 3.615 seconds
{noformat}
                
> Skip execution of queries with always false WHERE clauses
> ---------------------------------------------------------
>
>                 Key: HIVE-3006
>                 URL: https://issues.apache.org/jira/browse/HIVE-3006
>             Project: Hive
>          Issue Type: Improvement
>          Components: Query Processor
>            Reporter: Carl Steinbach
>


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