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Posted to dev@hive.apache.org by "Carl Steinbach (JIRA)" <ji...@apache.org> on 2012/05/06 03:41:47 UTC
[jira] [Commented] (HIVE-3006) Skip execution of queries with
always false WHERE clauses
[ 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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