vlsi commented on a change in pull request #2363:
URL: https://github.com/apache/calcite/pull/2363#discussion_r591572730



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File path: core/src/main/java/org/apache/calcite/rel/core/Sort.java
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@@ -124,11 +126,24 @@ public abstract Sort copy(RelTraitSet traitSet, RelNode 
newInput,
 
   @Override public @Nullable RelOptCost computeSelfCost(RelOptPlanner planner,
       RelMetadataQuery mq) {
+    double rowCount = mq.getRowCount(this);
+    if (collation.getFieldCollations().isEmpty()) {
+      return planner.getCostFactory().makeCost(rowCount, 0, 0);
+    }
+    final double inCount = mq.getRowCount(input);
     // Higher cost if rows are wider discourages pushing a project through a
     // sort.
-    final double rowCount = mq.getRowCount(this);
     final double bytesPerRow = getRowType().getFieldCount() * 4;

Review comment:
       > I have try to deal with above problem, but when I change it, some test 
failed. such as JdbcTest.testAlmostBushy
   
   What are the failures? Does the change improve things? Does it make plans 
worse?




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