[GitHub] [calcite] hbtoo commented on a change in pull request #1927: [CALCITE-3939] Change UnionEliminatorRule and ProjectRemoveRule to auto pruning SubstitutionRule

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

hbtoo commented on a change in pull request #1927:
URL: https://github.com/apache/calcite/pull/1927#discussion_r412360659



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File path: core/src/main/java/org/apache/calcite/rel/rules/UnionEliminatorRule.java
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@@ -44,18 +46,17 @@ public UnionEliminatorRule(Class<? extends Union> clazz,
 
   //~ Methods ----------------------------------------------------------------
 
-  public void onMatch(RelOptRuleCall call) {
+  @Override public boolean matches(RelOptRuleCall call) {
     Union union = call.rel(0);
-    if (union.getInputs().size() != 1) {
-      return;
-    }
-    if (!union.all) {
-      return;
-    }
-
-    // REVIEW jvs 14-Mar-2006:  why don't we need to register
-    // the equivalence here like we do in AggregateRemoveRule?
+    return union.all && union.getInputs().size() == 1;

Review comment:
       I guess one possible case is this. Unions are typically created via:
   public static LogicalUnion create(List<RelNode> inputs, boolean all);
   
   "List<RelNode> inputs" is typically assembled with a for loop. Whenever the for loop executes with only one loop, we have an input list of one element. 




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