groupedresult.java

hsqldb是100％java实现的数据库,是一个开放源代码的JAVA数据库 l 具有标准的SQL语法和JAVA接口 l HSQLDB可以自由使用和分发 l 非常简洁和快速的

/* Copyright (c) 2001-2005, The HSQL Development Group
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * Redistributions of source code must retain the above copyright notice, this
 * list of conditions and the following disclaimer.
 *
 * Redistributions in binary form must reproduce the above copyright notice,
 * this list of conditions and the following disclaimer in the documentation
 * and/or other materials provided with the distribution.
 *
 * Neither the name of the HSQL Development Group nor the names of its
 * contributors may be used to endorse or promote products derived from this
 * software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL HSQL DEVELOPMENT GROUP, HSQLDB.ORG,
 * OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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 */


package org.hsqldb;

import org.hsqldb.lib.ArrayUtil;
import org.hsqldb.lib.HashSet;
import org.hsqldb.lib.Iterator;

/**
 * This class is used for grouping select results, especially for select
 * statements that include group by clause and nested aggregate functions.
 * It is used by the <b>Select</b> class regardless the existence of group by
 * clause.
 * <p>
 * When a group by clause is defined, a <b>ResultGroup</b> is used to hold
 * all column values and <b>AggregatingValue</b>s for each group.  When a group
 * by clause is not defined, one <b>ResultGroup</b> is used to hold all the
 * results.<p>
 *
 * All <b>ResultGroup</b>s are placed in a <b>HashSet</b>.  Adding a new row
 * will first retrieve the corresponding group from the table, based on the
 * values in the group by columns.  If a group is found, then the row
 * associated with the group will be returned.  Otherwise a new group is
 * created with the new row, and the new row is returned.
 * <p>
 * The <b>Select</b> can then update the values and <b>AggregatingValue</b>s
 * in the returned row, rather than the original row.  This approach enables
 * nested aggregate functions, such as "count(id)+2, 20-count(id),
 * max(id)-min(id)" support.
 *
 * @author  Tony Lai
 * @version   1.7.2
 * @since   1.7.2
 * @see     Expression
 * @see     Select
 */

// fredt@users - patch 1.7.2 - mods to use new HashSet class and to separate addRow and getRow operations
class GroupedResult {

/** @todo fredt - initialise results on first use */
    private Result        result;
    int                   groupBegin;
    int                   groupEnd;
    private final boolean isGrouped;
    private final boolean isAggregated;
    private HashSet       groups;
    private ResultGroup   currGroup;

    GroupedResult(Select select, Result.ResultMetaData meta) {

        result       = new Result(meta);
        groupBegin   = select.iResultLen;
        groupEnd     = groupBegin + select.iGroupLen;
        isGrouped    = groupBegin != groupEnd;
        isAggregated = select.isAggregated;

        if (isGrouped) {
            groups = new HashSet();
        }
    }

    Object[] getRow(Object[] row) {

        if (isGrouped) {
            ResultGroup newGroup = new ResultGroup(row);
            ResultGroup group    = (ResultGroup) groups.get(newGroup);

            if (group != null) {
                ArrayUtil.copyArray(group.row, row, row.length);
            }
        } else if (isAggregated) {
            if (currGroup != null) {
                ArrayUtil.copyArray(currGroup.row, row, row.length);
            }
        }

        return row;
    }

    void addRow(Object[] row) {

        if (isGrouped) {
            ResultGroup newGroup = new ResultGroup(row);

            currGroup = (ResultGroup) groups.get(newGroup);

            if (currGroup == null) {
                currGroup = newGroup;

                groups.add(currGroup);
                result.add(row);
            } else {
                System.arraycopy(row, 0, currGroup.row, 0, row.length);
            }
        } else if (isAggregated) {
            if (currGroup == null) {
                currGroup = new ResultGroup(row);

                result.add(row);
            } else {
                System.arraycopy(row, 0, currGroup.row, 0, row.length);
            }
        } else {
            result.add(row);
        }
    }

    int size() {
        return result.getSize();
    }

    Iterator iterator() {
        return result.iterator();
    }

    Result getResult() {
        return result;
    }

    class ResultGroup {

        Object[] row;
        int      hashCode;

        private ResultGroup(Object[] row) {

            this.row = row;
            hashCode = 0;

            for (int i = groupBegin; i < groupEnd; i++) {
                if (row[i] != null) {
                    hashCode += row[i].hashCode();
                }
            }
        }

        public int hashCode() {
            return hashCode;
        }

        public boolean equals(Object obj) {

            if (obj == this) {
                return true;
            }

            if (obj == null ||!(obj instanceof ResultGroup)) {
                return false;
            }

            ResultGroup group = (ResultGroup) obj;

            for (int i = groupBegin; i < groupEnd; i++) {
                if (!equals(row[i], group.row[i])) {
                    return false;
                }
            }

            return true;
        }

        private boolean equals(Object o1, Object o2) {
            return (o1 == null) ? o2 == null
                                : o1.equals(o2);
        }
    }
}