Jinfeng Ni created DRILL-1061:
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Summary: Add or modify Optiq rule such that two projects involving
complex JSON objects should not be collapsed into one.
Key: DRILL-1061
URL: https://issues.apache.org/jira/browse/DRILL-1061
Project: Apache Drill
Issue Type: Bug
Reporter: Jinfeng Ni
Currently, Drill could not nest a function whose output is a complex JSON
object into another function directly. For instance,
select foo.mycol.x from (
select convert_from('{ x : [1,2], y : 100 }', 'JSON') as mycol
from cp.`tpch/nation.parquet`) as foo(mycol);
select convert_to(foo.mycol.x, 'JSON') from (
select convert_from('{ x : [1,2], y : 100 }', 'JSON') as mycol
from cp.`tpch/nation.parquet`) as foo(mycol);
Optiq will merge the project in the out subquery with the project in the inner
subquery into one project expression. This cause issues in Drill side.
In stead, we should add or modify Optiq rule so that the two projects will stay
where they are, and evaluate the convert_from () first and produce a record
batch. The second project will read from the record batch, and produce its
output.
Doing that will enable Drill to use out / inner subquery to refer the complex
JSON object .
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