[jira] [Created] (FLINK-19639) Support SupportsNestedProjectionPushDown in planner

["Shengkai Fang (Jira)" <ji...@apache.org>]

Shengkai Fang created FLINK-19639:
-------------------------------------

             Summary: Support SupportsNestedProjectionPushDown in planner
                 Key: FLINK-19639
                 URL: https://issues.apache.org/jira/browse/FLINK-19639
             Project: Flink
          Issue Type: New Feature
          Components: Table SQL / Planner
            Reporter: Shengkai Fang


Support to push nested projection into {{TableSourceScan}}. But it may cause name conflicts in some situaion. For example, we create table with ddl
{code:sql}
CREATE TABLE NestedTable (
     nest1 ROW<a INT>,
     nest2 ROW<a INT>
)
{code}
and with query
{code:sql}
SELECT nest1.a, nest2.a from NestedTable
{code}
and we will get 2 {{`a`}} in the new schema when pushing projection. 
 Here we use {{'_'}} to concatenate the names of all levels as the name of the nested fields. In this example, we will get fields {{nest1_a, nest2_a}} in the new schema.



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