alamb commented on code in PR #21362:
URL: https://github.com/apache/datafusion/pull/21362#discussion_r3066496405


##########
datafusion/sqllogictest/test_files/order.slt:
##########
@@ -1521,7 +1579,7 @@ query TT
 EXPLAIN SELECT c1, c2 FROM table_with_ordered_pk ORDER BY c1, c2;
 ----
 logical_plan
-01)Sort: table_with_ordered_pk.c1 ASC NULLS LAST, table_with_ordered_pk.c2 ASC 
NULLS LAST
+01)Sort: table_with_ordered_pk.c1 ASC NULLS LAST

Review Comment:
   I don't understand this change  -- the query requires `ORDR BY c1, c2` but 
now the query only sorts on c1. The primary key on `c1` means there are no 
duplicates, but  how does that ensure it is also ordered by `c2`
   
   For example what about
   
   ```sql
   INSERT INTO table VALUES (1,2)
   INSERT INTO table VALUES (2,1)
   ```
   
   That is still ordered by c1, but if you don't also sort of c2, you'll end up 
with the wrong sort



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