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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (KYLIN-3634) when filter column has null value may cause incorrect query result
Date Wed, 17 Oct 2018 06:25:00 GMT

    [ https://issues.apache.org/jira/browse/KYLIN-3634?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16653031#comment-16653031
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ASF GitHub Bot commented on KYLIN-3634:
---------------------------------------

asfgit commented on issue #292: KYLIN-3634 when filter column has null value may cause incorrect
query result
URL: https://github.com/apache/kylin/pull/292#issuecomment-430504606
 
 
   Can one of the admins verify this patch?

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> when filter column has null value may cause incorrect query result
> ------------------------------------------------------------------
>
>                 Key: KYLIN-3634
>                 URL: https://issues.apache.org/jira/browse/KYLIN-3634
>             Project: Kylin
>          Issue Type: Bug
>          Components: Query Engine
>    Affects Versions: v2.0.0
>            Reporter: WangBo
>            Priority: Major
>         Attachments: 0001-KYLIN-3634-when-filter-column-has-null-value-may-cau.patch
>
>
> h1. Question
> when a column has null value,and using it as a filter column when querying, and the
filter value is not exist in the table,this may cause incorrect result
> h1. An Example
> h2. Table A
> the table A has three rows,city column of one row has null value
>  
> ||day||...||city||price||
> |20180101| |null|10|
> |20180101| |beijing|20|
> |20180101| |shanghai|10|
> h2. Query SQL
> select day,sum(price) from a where city <> 'abc' group by day
> h2. Correct Result
> exclude the row contains null city value
> ||day||col||
> |20180101|30|
> h2. InCorrect Result
> resullt 0 rows
> this happens in our production environment,the kylin version is 2.0.0
> h1. Analysis process
> 1,city column dosen't have a value,so the CompareTupleFilter will turn into  ConstantTupleFilter(see
GTUtil.java)
> 2,if dimensions in the sql dosen't match all the columns using in group by,the  bytesComparator
used in hbase aggregation map will only compare the columns using in group by
> 3,when GTAggregateScanner constructs key of aggBufMap,the key may contains null value,because
the comparator of aggBufMap only compares group by columns,so the tuple share same group by
columns may also share the same keys which contains null value;This may cause kylin server
receives tuples contains null value;
> 4,when the code which dynamically generated by calcilte deals tuples using filter,it
first judges whether the column is null.Because filter column in the tuple contains null value,so
it always return false, no tuples will return.
> h1. Solution
> when the filter column value is a invalid means not in the table,turn the CompareTupleFiter
into IS_NOT_NULL filter,instead of ConstantTupleFilter.TURE
>  
> Now I have test the feature in our production environment ;
> test in “mvn test” had passed,but not test in sandbox
>  



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