[GitHub] [arrow-datafusion] jackwener commented on a diff in pull request #4753: Take the top level `schema` into account when creating `UnionExec`

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

jackwener commented on code in PR #4753:
URL: https://github.com/apache/arrow-datafusion/pull/4753#discussion_r1059230136


##########
datafusion/core/tests/sql/union.rs:
##########
@@ -80,6 +80,23 @@ async fn union_all_with_aggregate() -> Result<()> {
     Ok(())
 }
 
+#[tokio::test]
+async fn union_all_with_count() -> Result<()> {
+    let ctx = SessionContext::new();
+    execute_to_batches(&ctx, "CREATE table t as SELECT 1 as a").await;
+    let sql = "SELECT COUNT(*) FROM (SELECT a from t UNION ALL SELECT a from t)";

Review Comment:
   > BTW, I'm not sure if it was a bug, but the `PushDownProjection` doesn't push down the empty projection to the child plans of `Union` in this example. Maybe @jackwener knows more about it.
   
   we need an issue to track this problem, I think there are some different ways of dealing with this problem.



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