[GitHub] [calcite] sdreynolds commented on a diff in pull request #2848: [CALCITE-5201] Improve SemiJoinRule to match Join's right input which is unique for Join keys

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

sdreynolds commented on code in PR #2848:
URL: https://github.com/apache/calcite/pull/2848#discussion_r1026959819


##########
core/src/main/java/org/apache/calcite/rel/rules/SemiJoinRule.java:
##########
@@ -232,6 +234,84 @@ default JoinToSemiJoinRuleConfig withOperandFor(Class<Join> joinClass,
     }
   }
 
+  /**
+   * SemiJoinRule that matches a Project on top of a Join with a RelNode
+   * which is unique for Join's right keys.
+   *
+   * @see CoreRules#JOIN_ON_UNIQUE_TO_SEMI_JOIN */
+  public static class JoinOnUniqueToSemiJoinRule extends SemiJoinRule {
+
+    /** Creates a JoinOnUniqueToSemiJoinRule. */
+    protected JoinOnUniqueToSemiJoinRule(JoinOnUniqueToSemiJoinRuleConfig config) {
+      super(config);
+    }
+
+    @Override public boolean matches(RelOptRuleCall call) {
+      final Project project = call.rel(0);
+      final Join join = call.rel(1);
+      final RelNode left = call.rel(2);
+
+      final ImmutableBitSet bits =
+          RelOptUtil.InputFinder.bits(project.getProjects(), null);
+      final ImmutableBitSet rightBits =
+          ImmutableBitSet.range(left.getRowType().getFieldCount(),
+              join.getRowType().getFieldCount());
+      return !bits.intersects(rightBits);
+    }
+
+    @Override public void onMatch(RelOptRuleCall call) {
+      final Project project = call.rel(0);
+      final Join join = call.rel(1);
+      final RelNode left = call.rel(2);
+      final RelNode right = call.rel(3);
+
+      final JoinInfo joinInfo = join.analyzeCondition();
+      final RelOptCluster cluster = join.getCluster();
+      final RelMetadataQuery mq = cluster.getMetadataQuery();
+      final Boolean unique = mq.areColumnsUnique(right, joinInfo.rightSet());
+      if (unique != null && unique) {
+        final RelBuilder builder = call.builder();
+        switch (join.getJoinType()) {
+        case INNER:
+          builder.push(left);
+          builder.push(right);
+          builder.join(JoinRelType.SEMI, join.getCondition());
+          break;
+        case LEFT:
+          builder.push(left);
+          break;
+        default:
+          throw new AssertionError(join.getJoinType());
+        }
+        builder.project(project.getProjects());

Review Comment:
   :doh: this doesn't carry through the field aliases like it does in the other [rule](https://github.com/libenchao/calcite/blob/65e07f71c3e98115f114ee05986daa6baab28b96/core/src/main/java/org/apache/calcite/rel/rules/SemiJoinRule.java#L127)
   ```java
   builder.project(project.getProjects(), project.getRowType().getFieldNames());
   ```



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