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https://issues.apache.org/jira/browse/DRILL-5667?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Jinfeng Ni reassigned DRILL-5667:
---------------------------------
Assignee: Jinfeng Ni
> Project operator would change output field order if convertfromJSON is used
> ----------------------------------------------------------------------------
>
> Key: DRILL-5667
> URL: https://issues.apache.org/jira/browse/DRILL-5667
> Project: Apache Drill
> Issue Type: Bug
> Reporter: Jinfeng Ni
> Assignee: Jinfeng Ni
>
> When one of the projected expression uses convertfromJSON function, such
> expression would be put in the last of output fields. In general, such
> rearrange of output fields would not cause problem, since most of Drill's
> execution operators uses name-based resolution. However, union/union-all
> operators uses positional reference. If one branch of union/union-all
> re-arranges the output fields, while the other branch does not, then it would
> lead either incorrect query result, or execution error.
> For instance, given the following json file:
> {code}
> a: { b: 100, c : "DRILL"}}
> {code}
> The following query would fail with execution error:
> {code}
> select 'abc' as col1, convert_from(convert_to(t.a, 'JSON'), 'JSON') as col2,
> 'xyz' as col3
> from dfs.tmp.`1.json` t
> union all
> select 'abc' as col1, t.a as col2, 'xyz' as col3
> from dfs.tmp.`1.json` t;
> Error: SYSTEM ERROR: DrillRuntimeException: Type mismatch between VARCHAR on
> the left side and MAP on the right side in column 2 of UNION ALL
> {code}
> If we put the Map column as the last position in both of union all branches,
> the query will run successfully.
> {code}
> select 'abc' as col1, 'xyz' as col3, convert_from(convert_to(t.a, 'JSON'),
> 'JSON') as col2
> from dfs.tmp.`1.json` t
> union all
> select 'abc' as col1, 'xyz' as col3, t.a as col2
> from dfs.tmp.`1.json` t;
> +-------+-------+------------------------+
> | col1 | col3 | col2 |
> +-------+-------+------------------------+
> | abc | xyz | {"b":100,"c":"DRILL"} |
> | abc | xyz | {"b":100,"c":"DRILL"} |
> +-------+-------+------------------------+
> {code}
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