[GitHub] [arrow] waynexia commented on a change in pull request #8662: ARROW-9911: [Rust][DataFusion] SELECT with no FROM clause should produce a single row of output

[GitBox <gi...@apache.org>]

waynexia commented on a change in pull request #8662:
URL: https://github.com/apache/arrow/pull/8662#discussion_r523426357



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File path: rust/datafusion/src/physical_plan/projection.rs
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@@ -114,14 +117,33 @@ impl ExecutionPlan for ProjectionExec {
     }
 
     async fn execute(&self, partition: usize) -> Result<SendableRecordBatchStream> {
+        let input = if self.input.as_any().downcast_ref::<EmptyExec>().is_some() {

Review comment:
       I add this field in commit ef09e12.
   
   This flag is set in logical plan phase, `from_join_to_plan()`. If ast has no `FROM` clause then an `EmptyRelation` node will be added with `produce_one_row` set to true. And then comes to exec phase, `EmptyExec` will produce a placeholder row.
   
   Maybe this is better? :smiley: 




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