java/engine/org/apache/derby/impl/sql/compile/MaxMinAggregateDefinition.java

/*

   Derby - Class org.apache.derby.impl.sql.compile.MaxMinAggregateDefinition

   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.derby.impl.sql.compile;

import org.apache.derby.iapi.reference.ClassName;
import org.apache.derby.iapi.services.context.Context;
import org.apache.derby.iapi.services.context.ContextService;
import org.apache.derby.iapi.sql.conn.LanguageConnectionContext;
import org.apache.derby.iapi.types.DataTypeDescriptor;
import org.apache.derby.iapi.types.TypeId;

/**
 * Defintion for the MAX()/MIN() aggregates.
 *
 */
class MaxMinAggregateDefinition
		implements AggregateDefinition 
{
	private boolean isMax;
  
	/**
	 * Niladic constructor.  Does nothing.  For ease
	 * Of use, only.
	 */
    public MaxMinAggregateDefinition() { super(); }

	/**
	 * Determines the result datatype.  Accept NumberDataValues
	 * only.  
	 * <P>
	 * <I>Note</I>: In the future you should be able to do
	 * a sum user data types.  One option would be to run
	 * sum on anything that implements divide().  
	 *
	 * @param inputType	the input type, either a user type or a java.lang object
	 *
	 * @return the output Class (null if cannot operate on
	 *	value expression of this type.
	 */
	public final DataTypeDescriptor	getAggregator(DataTypeDescriptor inputType, 
				StringBuffer aggregatorClass) 
	{
		LanguageConnectionContext lcc = (LanguageConnectionContext)
			QueryTreeNode.getContext(LanguageConnectionContext.CONTEXT_ID);

			/*
			** MIN and MAX may return null
			*/
		DataTypeDescriptor dts = inputType.getNullabilityType(true);
		TypeId compType = dts.getTypeId();

		/*
		** If the class implements NumberDataValue, then we
		** are in business.  Return type is same as input
		** type.
		*/
		if (compType.orderable(
						lcc.getLanguageConnectionFactory().getClassFactory()))
		{
			aggregatorClass.append(ClassName.MaxMinAggregator);
			
			return dts;
		}
		return null;
	}

	/**
	 * This is set by the parser.
	 */
    final void setMaxOrMin(boolean isMax)
	{
		this.isMax = isMax;
	}

	/**
	 * Return if the aggregator class is for min/max.
	 *
	 * @return boolean true/false
	 */
    final boolean isMax()
	{
		return(isMax);
	}
    
}