content: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to you under the Apache License, Version 2.0
   * (the "License"); you may not use this file except in compliance with
   * the License.  You may obtain a copy of the License at
   *
   * http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.calcite.rel.rules;
  
  import org.apache.calcite.plan.Contexts;
  import org.apache.calcite.plan.RelOptCluster;
  import org.apache.calcite.plan.RelOptRuleCall;
  import org.apache.calcite.plan.RelRule;
  import org.apache.calcite.rel.RelNode;
  import org.apache.calcite.rel.core.CorrelationId;
  import org.apache.calcite.rel.core.Join;
  import org.apache.calcite.rel.core.RelFactories;
  import org.apache.calcite.rel.logical.LogicalCorrelate;
  import org.apache.calcite.rel.logical.LogicalJoin;
  import org.apache.calcite.rex.RexBuilder;
  import org.apache.calcite.rex.RexInputRef;
  import org.apache.calcite.rex.RexNode;
  import org.apache.calcite.rex.RexShuttle;
  import org.apache.calcite.tools.RelBuilder;
  import org.apache.calcite.tools.RelBuilderFactory;
  import org.apache.calcite.util.ImmutableBitSet;
  
  import org.immutables.value.Value;
  
  /**
   * Rule that converts a {@link org.apache.calcite.rel.core.Join}
   * into a {@link org.apache.calcite.rel.logical.LogicalCorrelate}, which can
   * then be implemented using nested loops.
   *
   * <p>For example,
   *
   * <blockquote><code>select * from emp join dept on emp.deptno =
   * dept.deptno</code></blockquote>
   *
   * <p>becomes a Correlator which restarts LogicalTableScan("DEPT") for each
   * row read from LogicalTableScan("EMP").
   *
   * <p>This rule is not applicable if for certain types of outer join. For
   * example,
   *
   * <blockquote><code>select * from emp right join dept on emp.deptno =
   * dept.deptno</code></blockquote>
   *
   * <p>would require emitting a NULL emp row if a certain department contained no
   * employees, and Correlator cannot do that.
   *
   * @see CoreRules#JOIN_TO_CORRELATE
   */
  @Value.Enclosing
  public class JoinToCorrelateRule
      extends RelRule<JoinToCorrelateRule.Config>
      implements TransformationRule {
  
    /** Creates a JoinToCorrelateRule. */
    protected JoinToCorrelateRule(Config config) {
      super(config);
    }
  
    @Deprecated // to be removed before 2.0
    public JoinToCorrelateRule(RelBuilderFactory relBuilderFactory) {
      this(Config.DEFAULT.withRelBuilderFactory(relBuilderFactory)
          .as(Config.class)
          .withOperandFor(LogicalJoin.class));
    }
  
    @Deprecated // to be removed before 2.0
    protected JoinToCorrelateRule(RelFactories.FilterFactory filterFactory) {
      this(Config.DEFAULT
          .withRelBuilderFactory(RelBuilder.proto(Contexts.of(filterFactory)))
          .as(Config.class)
          .withOperandFor(LogicalJoin.class));
    }
  
    //~ Methods ----------------------------------------------------------------
  
    @Override public boolean matches(RelOptRuleCall call) {
      Join join = call.rel(0);
      return !join.getJoinType().generatesNullsOnLeft();
    }
  
    @Override public void onMatch(RelOptRuleCall call) {
      assert matches(call);
      final Join join = call.rel(0);
      RelNode right = join.getRight();
      final RelNode left = join.getLeft();
      final int leftFieldCount = left.getRowType().getFieldCount();
      final RelOptCluster cluster = join.getCluster();
      final RexBuilder rexBuilder = cluster.getRexBuilder();
      final RelBuilder relBuilder = call.builder();
      final CorrelationId correlationId = cluster.createCorrel();
      final RexNode corrVar =
          rexBuilder.makeCorrel(left.getRowType(), correlationId);
      final ImmutableBitSet.Builder requiredColumns = ImmutableBitSet.builder();
  
      // Replace all references of left input with FieldAccess(corrVar, field)
      final RexNode joinCondition = join.getCondition().accept(new RexShuttle() {
        @Override public RexNode visitInputRef(RexInputRef input) {
          int field = input.getIndex();
          if (field >= leftFieldCount) {
            return rexBuilder.makeInputRef(input.getType(),
                input.getIndex() - leftFieldCount);
          }
          requiredColumns.set(field);
          return rexBuilder.makeFieldAccess(corrVar, field);
        }
      });
  
      relBuilder.push(right).filter(joinCondition);
  
      RelNode newRel =
          LogicalCorrelate.create(left,
              relBuilder.build(),
              join.getHints(),
              correlationId,
              requiredColumns.build(),
              join.getJoinType());
      call.transformTo(newRel);
    }
  
    /** Rule configuration. */
    @Value.Immutable
    public interface Config extends RelRule.Config {
      Config DEFAULT = ImmutableJoinToCorrelateRule.Config.of()
          .withOperandFor(LogicalJoin.class);
  
      @Override default JoinToCorrelateRule toRule() {
        return new JoinToCorrelateRule(this);
      }
  
      /** Defines an operand tree for the given classes. */
      default Config withOperandFor(Class<? extends Join> joinClass) {
        return withOperandSupplier(b -> b.operand(joinClass).anyInputs())
            .as(Config.class);
      }
    }
  }
  