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.asterix.optimizer.rules;
  
  import org.apache.asterix.om.base.ABoolean;
  import org.apache.asterix.om.constants.AsterixConstantValue;
  import org.apache.commons.lang3.mutable.Mutable;
  import org.apache.hyracks.algebricks.common.exceptions.AlgebricksException;
  import org.apache.hyracks.algebricks.core.algebra.base.ILogicalExpression;
  import org.apache.hyracks.algebricks.core.algebra.base.ILogicalOperator;
  import org.apache.hyracks.algebricks.core.algebra.base.IOptimizationContext;
  import org.apache.hyracks.algebricks.core.algebra.base.LogicalOperatorTag;
  import org.apache.hyracks.algebricks.core.algebra.expressions.ConstantExpression;
  import org.apache.hyracks.algebricks.core.algebra.operators.logical.AbstractLogicalOperator;
  import org.apache.hyracks.algebricks.core.algebra.operators.logical.SelectOperator;
  import org.apache.hyracks.algebricks.core.rewriter.base.IAlgebraicRewriteRule;
  
  /**
   * This rule removes redundant select operator, e.g., select operators
   * in which the condition is TRUE.
   * Note that the ConstantFoldingRule will evaluate the condition expression
   * during compile time if it is possible.
   *
   * @author yingyib
   */
  public class RemoveRedundantSelectRule implements IAlgebraicRewriteRule {
  
      @Override
      public boolean rewritePre(Mutable<ILogicalOperator> opRef, IOptimizationContext context)
              throws AlgebricksException {
          return false;
      }
  
      @Override
      public boolean rewritePost(Mutable<ILogicalOperator> opRef, IOptimizationContext context)
              throws AlgebricksException {
          AbstractLogicalOperator op = (AbstractLogicalOperator) opRef.getValue();
          if (op.getOperatorTag() != LogicalOperatorTag.SELECT) {
              return false;
          }
          SelectOperator select = (SelectOperator) op;
          ILogicalExpression cond = select.getCondition().getValue();
          if (alwaysHold(cond)) {
              opRef.setValue(select.getInputs().get(0).getValue());
              return true;
          }
          return false;
      }
  
      /**
       * Whether the condition expression always returns true.
       *
       * @param cond
       * @return true if the condition always holds; false otherwise.
       */
      private boolean alwaysHold(ILogicalExpression cond) {
          if (cond.equals(ConstantExpression.TRUE)) {
              return true;
          }
          if (cond.equals(new ConstantExpression(new AsterixConstantValue(ABoolean.TRUE)))) {
              return true;
          }
          return false;
      }
  }
  