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https://issues.apache.org/jira/browse/KYLIN-4041?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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nichunen resolved KYLIN-4041.
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Resolution: Fixed
> CONCAT NULL not working properly
> --------------------------------
>
> Key: KYLIN-4041
> URL: https://issues.apache.org/jira/browse/KYLIN-4041
> Project: Kylin
> Issue Type: Improvement
> Reporter: Yifei Wu
> Assignee: Yifei Wu
> Priority: Major
> Fix For: v3.0.0-alpha2
>
>
> to support SQL 'concat' function, Kylin introduces a UDF named ConcatUDF.
> but the NULL case cannot deal with correctly, like the below sql:
> ```
> select
> concat(meta_categ_name, CAST(null as VARCHAR)) as c1,
> concat(meta_categ_name, ' Catagory') as c2
> from test_kylin_fact
> left JOIN edw.test_cal_dt as test_cal_dt
> ON test_kylin_fact.cal_dt = test_cal_dt.cal_dt
> left JOIN test_category_groupings
> ON test_kylin_fact.leaf_categ_id = test_category_groupings.leaf_categ_id AND
> test_kylin_fact.lstg_site_id = test_category_groupings.site_id
> left JOIN edw.test_sites as test_sites
> ON test_kylin_fact.lstg_site_id = test_sites.site_id
> where meta_categ_name = 'Computers'
> group by meta_categ_name
> order by meta_categ_name
> limit 1
> ```
> when CONCAT value with NULL, the result is expected to be still NULL.
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