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From "Aman Sinha (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-2328) Concat operator returns wrong result when one of the operands is NULL
Date Sat, 28 Feb 2015 19:22:04 GMT

    [ https://issues.apache.org/jira/browse/DRILL-2328?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14341737#comment-14341737
] 

Aman Sinha commented on DRILL-2328:
-----------------------------------

+1.  One observation: since concatOperator ('||') and concat function have the same logic
in FunctionTemplate except for the NULL_IF_NULL attribute, it would have been nice to share
the code between them but I don't think the current framework allows that, so I am good with
your implementation for now. 

> 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: Aman Sinha
>            Priority: Critical
>         Attachments: DRILL-2328.1.patch
>
>
> 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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