2010YOUY01 commented on code in PR #27393:
URL: https://github.com/apache/datafusion/pull/27393#discussion_r4570476909


##########
datafusion/sqllogictest/test_files/copy.slt:
##########
@@ -823,3 +823,46 @@ physical_plan
 
 statement count 0
 drop table t;
+
+# COPY (... UNION ALL ... ORDER BY) must write rows in ORDER BY order when
+# each UNION ALL arm selects a different literal and reads an already sorted
+# input. The literal is constant within each arm but not across arms, so it
+# must stay in the merge key.
+#
+# Earlier versions reported only [ts ASC NULLS LAST] as the merge key in 
SortPreservingMergeExec due to issues with the
+# constants in the individual partitions.
+
+statement ok
+COPY (SELECT * FROM (VALUES (1, 10.0), (2, 20.0), (3, 30.0)) AS v(ts, x) ORDER 
BY ts)

Review Comment:
   good point, 
[d669651](https://github.com/apache/datafusion/pull/27393/commits/d669651801149cbd1f759891e329cb6383ac4651)



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