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.RelOptRuleCall;
  import org.apache.calcite.plan.RelRule;
  import org.apache.calcite.rel.RelNode;
  import org.apache.calcite.rel.core.Join;
  import org.apache.calcite.rel.core.JoinRelType;
  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.rex.RexUtil;
  import org.apache.calcite.sql.fun.SqlStdOperatorTable;
  import org.apache.calcite.tools.RelBuilder;
  
  import com.google.common.collect.ImmutableList;
  
  import org.immutables.value.Value;
  
  /**
   * Planner rule that matches a {@link Join}
   * that join type is FULL, and convert it to
   * a LEFT JOIN and RIGHT JOIN combination
   * with a UNION ALL above them.
   *
   * <p>The SQL example is as follows:
   *
   * <pre>{@code
   * SELECT *
   * FROM Employees e
   * FULL JOIN Departments d ON e.id = d.id
   * }</pre>
   *
   * <p>rewritten into
   *
   * <pre>{@code
   * SELECT *
   * FROM Employees e
   * LEFT JOIN Departments d ON e.id = d.id
   * UNION ALL
   * SELECT *
   * FROM Employees e
   * RIGHT JOIN Departments d ON e.id = d.id
   * WHERE (e.id = d.id) IS NOT TRUE;
   * }</pre>
   */
  @Value.Enclosing
  public class FullToLeftAndRightJoinRule
      extends RelRule<FullToLeftAndRightJoinRule.Config>
      implements TransformationRule {
  
    /** Creates an FullToLeftAndRightJoinRule. */
    protected FullToLeftAndRightJoinRule(Config config) {
      super(config);
    }
  
    //~ Methods ----------------------------------------------------------------
  
    @Override public void onMatch(RelOptRuleCall call) {
      final Join join = call.rel(0);
      RelBuilder relBuilder = call.builder();
  
      if (!RexUtil.isDeterministic(join.getCondition())) {
        return;
      }
  
      RexBuilder rexBuilder = relBuilder.getRexBuilder();
      RexNode newCondition =
          rexBuilder.makeCall(SqlStdOperatorTable.IS_NOT_TRUE, join.getCondition());
  
      final RexShuttle shuttle = new RexShuttle() {
        @Override public RexNode visitInputRef(RexInputRef inputRef) {
          return RexInputRef.of(inputRef.getIndex(), join.getRowType());
        }
      };
      newCondition = shuttle.apply(newCondition);
  
      RelNode newLeft = relBuilder.push(join.getLeft())
          .push(join.getRight())
          .join(JoinRelType.LEFT, join.getCondition())
          .build();
      RelNode newRight = relBuilder.push(join.getLeft())
          .push(join.getRight())
          .join(JoinRelType.RIGHT, join.getCondition())
          .filter(newCondition)
          .build();
  
      relBuilder.pushAll(ImmutableList.of(newLeft, newRight))
          .union(true);
  
      call.transformTo(relBuilder.build());
    }
  
    /** Rule configuration. */
    @Value.Immutable
    public interface Config extends RelRule.Config {
      Config DEFAULT = ImmutableFullToLeftAndRightJoinRule.Config.of()
          .withOperandFor(Join.class);
  
      @Override default FullToLeftAndRightJoinRule toRule() {
        return new FullToLeftAndRightJoinRule(this);
      }
  
      /** Defines an operand tree for the given classes. */
      default Config withOperandFor(Class<? extends Join> joinClass) {
        return withOperandSupplier(b -> b.operand(joinClass)
            .predicate(join -> join.getJoinType() == JoinRelType.FULL)
            .anyInputs())
            .as(Config.class);
      }
    }
  }
  