[GitHub] [calcite] chunweilei commented on a change in pull request #1707: [CALCITE-3649] Hints should be propagated correctly in planner rules …

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chunweilei commented on a change in pull request #1707: [CALCITE-3649] Hints should be propagated correctly in planner rules …
URL: https://github.com/apache/calcite/pull/1707#discussion_r362137407
 
 

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 File path: core/src/main/java/org/apache/calcite/plan/RelOptUtil.java
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 @@ -396,15 +396,60 @@ public static void verifyTypeEquivalence(
    * Copy the {@link org.apache.calcite.rel.hint.RelHint}s from {@code originalRel}
    * to {@code newRel} if both of them are {@link Hintable}.
    *
-   * <p>The hints are filtered by the hint strategies when attaching to the {@code newRel}.
+   * <p>The two relational expressions are assumed as semantically equivalent,
+   * that means the hints should be attached to the relational expression
+   * that expects to have them.
+   *
+   * <p>In order to achieve this, we do the following now:
+   *
+   * <ol>
+   *   <li>If the {@code originalRel} is not Project but {@code newRel} is,
+   *   try to copy the hints to the {@code newRel}'s input, this is needed because
 
 Review comment:
   `is` seems redundant.

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