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From "Carl Steinbach (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-3005) Query containing "LIMIT 0" clause should skip execution phase
Date Sun, 06 May 2012 01:29:47 GMT

    [ https://issues.apache.org/jira/browse/HIVE-3005?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13269099#comment-13269099
] 

Carl Steinbach commented on HIVE-3005:
--------------------------------------

Executing a query that contains a "LIMIT 0" clause is a trick that some clients (e.g. ODBC
clients) employ in order to generate a result set without incurring the cost of actually executing
the query. Unfortunately, this trick doesn't work with Hive:

{noformat}
hive> SELECT key FROM SRC LIMIT 0;
SELECT key FROM SRC LIMIT 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_20120505182828_a5405bcb-c156-4572-b2d8-eda2cc199a14.log
Job running in-process (local Hadoop)
Hadoop job information for null: number of mappers: 0; number of reducers: 0
2012-05-05 18:28:35,999 null map = 100%,  reduce = 0%
Ended Job = job_local_0001
Execution completed successfully
Mapred Local Task Succeeded . Convert the Join into MapJoin
OK
{noformat}

                
> Query containing "LIMIT 0" clause should skip execution phase
> -------------------------------------------------------------
>
>                 Key: HIVE-3005
>                 URL: https://issues.apache.org/jira/browse/HIVE-3005
>             Project: Hive
>          Issue Type: Improvement
>          Components: Query Processor
>            Reporter: Carl Steinbach
>


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