[jira] [Created] (KYLIN-3490) For some single column related queries, don't need to query cuboids, only dictionaries are enough

["Zhong Yanghong (JIRA)" <ji...@apache.org>]

Zhong Yanghong created KYLIN-3490:
-------------------------------------

             Summary: For some single column related queries, don't need to query cuboids, only dictionaries are enough
                 Key: KYLIN-3490
                 URL: https://issues.apache.org/jira/browse/KYLIN-3490
             Project: Kylin
          Issue Type: Improvement
            Reporter: Zhong Yanghong


A common use case for BI tools is as follows:
# Firstly, extract all of the values of a dimension column
# Then, select part of the values as filter condition.

Previously query for the first step requires to hit all of the segments' cuboid data, which may not be efficient, especially when the segments occupy many regions. 

To use dictionary rather than cuboid data to answer this kind of queries, will reduce the cost of many rpcs to hbase.

Sample queries are as follows:
{code}
select A
from T
group by A
{code}
{code}
select distinct A
from T
{code}
{code}
select max(A)
from T
{code}



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