[GitHub] [hive] kasakrisz commented on a diff in pull request #4253: HIVE-27278: Simplify correlated queries with empty inputs

["kasakrisz (via GitHub)" <gi...@apache.org>]

kasakrisz commented on code in PR #4253:
URL: https://github.com/apache/hive/pull/4253#discussion_r1176138739


##########
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/rules/HiveRemoveEmptySingleRules.java:
##########
@@ -192,6 +178,79 @@ public interface JoinRightEmptyRuleConfig extends PruneEmptyRule.Config {
     }
   }
 
+  private static RelNode padWithNulls(RelBuilder builder, RelNode input, RelDataType resultType,
+      boolean leftPadding) {
+    int padding = resultType.getFieldCount() - input.getRowType().getFieldCount();
+    List<RexNode> nullLiterals = Collections.nCopies(padding, builder.literal(null));
+    builder.push(input);
+    if (leftPadding) {
+      builder.project(concat(nullLiterals, builder.fields()));
+    } else {
+      builder.project(concat(builder.fields(), nullLiterals));
+    }
+    return builder.convert(resultType, true).build();
+  }
+
+  public static final RelOptRule CORRELATE_RIGHT_INSTANCE = RelRule.Config.EMPTY
+      .withOperandSupplier(b0 ->
+          b0.operand(Correlate.class).inputs(
+              b1 -> b1.operand(RelNode.class).anyInputs(),
+              b2 -> b2.operand(Values.class).predicate(Values::isEmpty).noInputs()))
+      .withDescription("PruneEmptyCorrelate(right)")
+      .withRelBuilderFactory(HiveRelFactories.HIVE_BUILDER)
+      .as(CorrelateEmptyRuleConfig.class)
+      .toRule();
+  public static final RelOptRule CORRELATE_LEFT_INSTANCE = RelRule.Config.EMPTY
+      .withOperandSupplier(b0 ->
+          b0.operand(Correlate.class).inputs(
+              b1 -> b1.operand(Values.class).predicate(Values::isEmpty).noInputs(),
+              b2 -> b2.operand(RelNode.class).anyInputs()))
+      .withDescription("PruneEmptyCorrelate(left)")
+      .withRelBuilderFactory(HiveRelFactories.HIVE_BUILDER)
+      .as(CorrelateEmptyRuleConfig.class)
+      .toRule();
+  
+  /** Configuration for rule that prunes a correlate if one of its inputs is empty. */
+  public interface CorrelateEmptyRuleConfig extends PruneEmptyRule.Config {

Review Comment:
   nit: should the implementation of this class go into two separate classes since there is no common parts of handling left and right empty inputs?



##########
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/rules/HiveRemoveEmptySingleRules.java:
##########
@@ -192,6 +178,79 @@ public interface JoinRightEmptyRuleConfig extends PruneEmptyRule.Config {
     }
   }
 
+  private static RelNode padWithNulls(RelBuilder builder, RelNode input, RelDataType resultType,
+      boolean leftPadding) {

Review Comment:
   nit: you can get rid of the flag argument `leftPadding` by creating two methods each of them responsible only for one type of padding:
   ```
   leftPadWithNulls(RelBuilder builder, RelNode input, RelDataType resultType)
   rightPadWithNulls(RelBuilder builder, RelNode input, RelDataType resultType)
   ```



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