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https://issues.apache.org/jira/browse/HIVE-10568?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14537371#comment-14537371
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Lefty Leverenz commented on HIVE-10568:
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Doc note: This adds *hive.optimize.distinct.rewrite* to HiveConf.java, so it
needs to be documented in the wiki. Perhaps it belongs in the UDFs doc as well
as Configs.
* [Configuration Properties -- Query and DDL Execution |
https://cwiki.apache.org/confluence/display/Hive/Configuration+Properties#ConfigurationProperties-QueryandDDLExecution]
* [Built-in Aggregate Functions (UDAF) |
https://cwiki.apache.org/confluence/display/Hive/LanguageManual+UDF#LanguageManualUDF-Built-inAggregateFunctions(UDAF)]
> Select count(distinct()) can have more optimal execution plan
> -------------------------------------------------------------
>
> Key: HIVE-10568
> URL: https://issues.apache.org/jira/browse/HIVE-10568
> Project: Hive
> Issue Type: Improvement
> Components: CBO, Logical Optimizer
> Affects Versions: 0.6.0, 0.7.0, 0.8.0, 0.9.0, 0.10.0, 0.11.0, 0.12.0,
> 0.13.0, 0.14.0, 1.0.0, 1.1.0
> Reporter: Mostafa Mokhtar
> Assignee: Ashutosh Chauhan
> Labels: TODOC1.2
> Fix For: 1.2.0
>
> Attachments: HIVE-10568.1.patch, HIVE-10568.2.patch,
> HIVE-10568.patch, HIVE-10568.patch
>
>
> {code:sql}
> select count(distinct ss_ticket_number) from store_sales;
> {code}
> can be rewritten as
> {code:sql}
> select count(1) from (select distinct ss_ticket_number from store_sales) a;
> {code}
> which may run upto 3x faster
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