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.core;
  
  import org.apache.calcite.plan.RelOptCluster;
  import org.apache.calcite.plan.RelOptCost;
  import org.apache.calcite.plan.RelOptPlanner;
  import org.apache.calcite.plan.RelOptUtil;
  import org.apache.calcite.plan.RelTraitSet;
  import org.apache.calcite.rel.BiRel;
  import org.apache.calcite.rel.RelInput;
  import org.apache.calcite.rel.RelNode;
  import org.apache.calcite.rel.RelWriter;
  import org.apache.calcite.rel.hint.Hintable;
  import org.apache.calcite.rel.hint.RelHint;
  import org.apache.calcite.rel.metadata.RelMetadataQuery;
  import org.apache.calcite.rel.type.RelDataType;
  import org.apache.calcite.sql.validate.SqlValidatorUtil;
  import org.apache.calcite.util.ImmutableBitSet;
  import org.apache.calcite.util.Litmus;
  
  import com.google.common.collect.ImmutableList;
  import com.google.common.collect.ImmutableSet;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.util.List;
  import java.util.Set;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * A relational operator that performs nested-loop joins.
   *
   * <p>It behaves like a kind of {@link org.apache.calcite.rel.core.Join},
   * but works by setting variables in its environment and restarting its
   * right-hand input.
   *
   * <p>Correlate is not a join since: typical rules should not match Correlate.
   *
   * <p>A Correlate is used to represent a correlated query. One
   * implementation strategy is to de-correlate the expression.
   *
   * <table>
   *   <caption>Mapping of physical operations to logical ones</caption>
   *   <tr><th>Physical operation</th><th>Logical operation</th></tr>
   *   <tr><td>NestedLoops</td><td>Correlate(A, B, regular)</td></tr>
   *   <tr><td>NestedLoopsOuter</td><td>Correlate(A, B, outer)</td></tr>
   *   <tr><td>NestedLoopsSemi</td><td>Correlate(A, B, semi)</td></tr>
   *   <tr><td>NestedLoopsAnti</td><td>Correlate(A, B, anti)</td></tr>
   *   <tr><td>HashJoin</td><td>EquiJoin(A, B)</td></tr>
   *   <tr><td>HashJoinOuter</td><td>EquiJoin(A, B, outer)</td></tr>
   *   <tr><td>HashJoinSemi</td><td>SemiJoin(A, B, semi)</td></tr>
   *   <tr><td>HashJoinAnti</td><td>SemiJoin(A, B, anti)</td></tr>
   * </table>
   *
   * @see CorrelationId
   */
  public abstract class Correlate extends BiRel implements Hintable {
    //~ Instance fields --------------------------------------------------------
  
    protected final CorrelationId correlationId;
    protected final ImmutableBitSet requiredColumns;
    protected final JoinRelType joinType;
    protected final ImmutableList<RelHint> hints;
  
    //~ Constructors -----------------------------------------------------------
  
    /**
     * Creates a Correlate.
     *
     * @param cluster      Cluster this relational expression belongs to
     * @param left         Left input relational expression
     * @param right        Right input relational expression
     * @param correlationId Variable name for the row of left input
     * @param requiredColumns Set of columns that are used by correlation
     * @param joinType Join type
     */
    @SuppressWarnings("method.invocation.invalid")
    protected Correlate(
        RelOptCluster cluster,
        RelTraitSet traitSet,
        List<RelHint> hints,
        RelNode left,
        RelNode right,
        CorrelationId correlationId,
        ImmutableBitSet requiredColumns,
        JoinRelType joinType) {
      super(cluster, traitSet, left, right);
      assert !joinType.generatesNullsOnLeft() : "Correlate has invalid join type " + joinType;
      this.joinType = requireNonNull(joinType, "joinType");
      this.correlationId = requireNonNull(correlationId, "correlationId");
      this.requiredColumns = requireNonNull(requiredColumns, "requiredColumns");
      this.hints = ImmutableList.copyOf(hints);
      assert isValid(Litmus.THROW, null);
    }
  
    @Deprecated // to be removed before 2.0
    protected Correlate(
        RelOptCluster cluster,
        RelTraitSet traitSet,
        RelNode left,
        RelNode right,
        CorrelationId correlationId,
        ImmutableBitSet requiredColumns,
        JoinRelType joinType) {
      this(cluster, traitSet, ImmutableList.of(), left, right,
          correlationId, requiredColumns, joinType);
    }
  
    /**
     * Creates a Correlate by parsing serialized output.
     *
     * @param input Input representation
     */
    protected Correlate(RelInput input) {
      this(
          input.getCluster(), input.getTraitSet(), input.getInputs().get(0),
          input.getInputs().get(1),
          new CorrelationId(
              requireNonNull((Integer) input.get("correlation"), "correlation")),
          input.getBitSet("requiredColumns"),
          requireNonNull(input.getEnum("joinType", JoinRelType.class), "joinType"));
    }
  
    //~ Methods ----------------------------------------------------------------
  
    @Override public boolean isValid(Litmus litmus, @Nullable Context context) {
      ImmutableBitSet leftColumns = ImmutableBitSet.range(left.getRowType().getFieldCount());
      return super.isValid(litmus, context)
          && litmus.check(leftColumns.contains(requiredColumns),
          "Required columns {} not subset of left columns {}", requiredColumns, leftColumns)
          && RelOptUtil.notContainsCorrelation(left, correlationId, litmus);
    }
  
    @Override public Correlate copy(RelTraitSet traitSet, List<RelNode> inputs) {
      assert inputs.size() == 2;
      return copy(traitSet,
          inputs.get(0),
          inputs.get(1),
          correlationId,
          requiredColumns,
          joinType);
    }
  
    public abstract Correlate copy(RelTraitSet traitSet,
        RelNode left, RelNode right, CorrelationId correlationId,
        ImmutableBitSet requiredColumns, JoinRelType joinType);
  
    public JoinRelType getJoinType() {
      return joinType;
    }
  
    @Override protected RelDataType deriveRowType() {
      switch (joinType) {
      case LEFT:
      case INNER:
        return SqlValidatorUtil.deriveJoinRowType(left.getRowType(),
            right.getRowType(), joinType,
            getCluster().getTypeFactory(), null,
            ImmutableList.of());
      case ANTI:
      case SEMI:
        return left.getRowType();
      default:
        throw new IllegalStateException("Unknown join type " + joinType);
      }
    }
  
    @Override public RelWriter explainTerms(RelWriter pw) {
      return super.explainTerms(pw)
          .item("correlation", correlationId)
          .item("joinType", joinType.lowerName)
          .item("requiredColumns", requiredColumns);
    }
  
    /**
     * Returns the correlating expressions.
     *
     * @return correlating expressions
     */
    public CorrelationId getCorrelationId() {
      return correlationId;
    }
  
    @Override public String getCorrelVariable() {
      return correlationId.getName();
    }
  
    /**
     * Returns the required columns in left relation required for the correlation
     * in the right.
     *
     * @return columns in left relation required for the correlation in the right
     */
    public ImmutableBitSet getRequiredColumns() {
      return requiredColumns;
    }
  
    @Override public Set<CorrelationId> getVariablesSet() {
      return ImmutableSet.of(correlationId);
    }
  
    @Override public double estimateRowCount(RelMetadataQuery mq) {
      double leftRowCount = mq.getRowCount(left);
      switch (joinType) {
      case SEMI:
      case ANTI:
        return leftRowCount;
      default:
        return leftRowCount * mq.getRowCount(right);
      }
    }
  
    @Override public @Nullable RelOptCost computeSelfCost(RelOptPlanner planner,
        RelMetadataQuery mq) {
      double rowCount = mq.getRowCount(this);
  
      final double rightRowCount = mq.getRowCount(right);
      final double leftRowCount = mq.getRowCount(left);
      if (Double.isInfinite(leftRowCount) || Double.isInfinite(rightRowCount)) {
        return planner.getCostFactory().makeInfiniteCost();
      }
  
      Double restartCount = mq.getRowCount(getLeft());
      if (restartCount == null) {
        return planner.getCostFactory().makeInfiniteCost();
      }
      // RelMetadataQuery.getCumulativeCost(getRight()); does not work for
      // RelSubset, so we ask planner to cost-estimate right relation
      RelOptCost rightCost = planner.getCost(getRight(), mq);
      if (rightCost == null) {
        return planner.getCostFactory().makeInfiniteCost();
      }
      RelOptCost rescanCost =
          rightCost.multiplyBy(Math.max(1.0, restartCount - 1));
  
      return planner.getCostFactory().makeCost(
          rowCount /* generate results */ + leftRowCount /* scan left results */,
          0, 0).plus(rescanCost);
    }
  
    @Override public ImmutableList<RelHint> getHints() {
      return hints;
    }
  }
  