WangBo created KYLIN-3634:
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Summary: 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
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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