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https://issues.apache.org/jira/browse/HIVE-18108?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16264640#comment-16264640
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Ashutosh Chauhan commented on HIVE-18108:
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+1
> in case basic stats are missing; rowcount estimation depends on the selected
> columns size
> -----------------------------------------------------------------------------------------
>
> Key: HIVE-18108
> URL: https://issues.apache.org/jira/browse/HIVE-18108
> Project: Hive
> Issue Type: Sub-task
> Reporter: Zoltan Haindrich
> Assignee: Zoltan Haindrich
> Attachments: HIVE-18108.01.patch
>
>
> in case basicstats are not available (especially rowcount):
> {code}
> set hive.stats.autogather=false;
> create table t (a integer, b string);
> insert into t values (1,'asd1');
> insert into t values (2,'asd2');
> insert into t values (3,'asd3');
> insert into t values (4,'asd4');
> insert into t values (5,'asd5');
> explain select a,count(1) from t group by a;
> -- estimated to read 8 rows from table t
> explain select b,count(1) from t group by b;
> -- estimated: 1 rows
> explain select a,b,count(1) from t group by a,b;
> -- estimated: 1 rows
> {code}
> it may not depend on the actually selected column set.
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