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From "WangBo (JIRA)" <>
Subject [jira] [Created] (KYLIN-3634) when filter column has null value may cause incorrect query result
Date Wed, 17 Oct 2018 06:02:00 GMT
WangBo created KYLIN-3634:

             Summary: when filter column has null value may cause incorrect query result
                 Key: KYLIN-3634
             Project: Kylin
          Issue Type: Bug
          Components: Query Engine
    Affects Versions: v2.0.0
            Reporter: WangBo

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

|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
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

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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