[jira] [Created] (KYLIN-4041) CONCAT NULL not working properly

["Yifei Wu (JIRA)" <ji...@apache.org>]

Yifei Wu created KYLIN-4041:
-------------------------------

             Summary: 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


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
```



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