[jira] [Created] (DRILL-2328) Concat operator returns wrong result when one of the operands is NULL

["Victoria Markman (JIRA)" <ji...@apache.org>]

Victoria Markman created DRILL-2328:
---------------------------------------

             Summary: Concat operator returns wrong result when one of the operands is NULL
                 Key: DRILL-2328
                 URL: https://issues.apache.org/jira/browse/DRILL-2328
             Project: Apache Drill
          Issue Type: Bug
          Components: Query Planning & Optimization
    Affects Versions: 0.8.0
            Reporter: Victoria Markman
            Assignee: Sean Hsuan-Yi Chu
            Priority: Critical


Queries below should return NULL:

{code}
0: jdbc:drill:schema=dfs> select cast(null as varchar(10)) || '--' from t1;
+------------+
|   EXPR$0   |
+------------+
| --         |
| --         |
| --         |
| --         |
| --         |
| --         |
| --         |
| --         |
| --         |
| --         |
+------------+
10 rows selected (0.09 seconds)
0: jdbc:drill:schema=dfs> select a1 || '--' from t1 where a1 is null;
+------------+
|   EXPR$0   |
+------------+
| --         |
+------------+
1 row selected (0.105 seconds)
{code}

Looks harmless at first, but a very common pattern in many customer queries will be broken: grouping by using '||' as following:

{code}
select
        cast(extract(day from c_timestamp) as varchar(10)) || '-' || cast(extract(month from c_timestamp) as varchar(10)) || '-' || cast(extract(year from c_timestamp) as varchar(10)),
        sum(c_integer)  as sum1
from
        alltypes_with_nulls
group by
        cast(extract(day from c_timestamp) as varchar(10)) || '-' || cast(extract(month from c_timestamp) as varchar(10)) || '-' || cast(extract(year from c_timestamp) as varchar(10))
order by
        cast(extract(day from c_timestamp) as varchar(10)) || '-' || cast(extract(month from c_timestamp) as varchar(10)) || '-' || cast(extract(year from c_timestamp) as varchar(10))
;
{code}




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