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From "Zoltan Haindrich (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HIVE-18108) in case basic stats are missing; rowcount estimation depends on the select columns size
Date Mon, 20 Nov 2017 15:27:00 GMT
Zoltan Haindrich created HIVE-18108:
---------------------------------------

             Summary: in case basic stats are missing; rowcount estimation depends on the
select columns size
                 Key: HIVE-18108
                 URL: https://issues.apache.org/jira/browse/HIVE-18108
             Project: Hive
          Issue Type: Sub-task
            Reporter: Zoltan Haindrich


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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