001: package com.quadcap.sql;
002:
003: /* Copyright 1999 - 2003 Quadcap Software. All rights reserved.
004: *
005: * This software is distributed under the Quadcap Free Software License.
006: * This software may be used or modified for any purpose, personal or
007: * commercial. Open Source redistributions are permitted. Commercial
008: * redistribution of larger works derived from, or works which bundle
009: * this software requires a "Commercial Redistribution License"; see
010: * http://www.quadcap.com/purchase.
011: *
012: * Redistributions qualify as "Open Source" under one of the following terms:
013: *
014: * Redistributions are made at no charge beyond the reasonable cost of
015: * materials and delivery.
016: *
017: * Redistributions are accompanied by a copy of the Source Code or by an
018: * irrevocable offer to provide a copy of the Source Code for up to three
019: * years at the cost of materials and delivery. Such redistributions
020: * must allow further use, modification, and redistribution of the Source
021: * Code under substantially the same terms as this license.
022: *
023: * Redistributions of source code must retain the copyright notices as they
024: * appear in each source code file, these license terms, and the
025: * disclaimer/limitation of liability set forth as paragraph 6 below.
026: *
027: * Redistributions in binary form must reproduce this Copyright Notice,
028: * these license terms, and the disclaimer/limitation of liability set
029: * forth as paragraph 6 below, in the documentation and/or other materials
030: * provided with the distribution.
031: *
032: * The Software is provided on an "AS IS" basis. No warranty is
033: * provided that the Software is free of defects, or fit for a
034: * particular purpose.
035: *
036: * Limitation of Liability. Quadcap Software shall not be liable
037: * for any damages suffered by the Licensee or any third party resulting
038: * from use of the Software.
039: */
040:
041: import java.io.IOException;
042:
043: import java.util.Vector;
044:
045: import java.sql.SQLException;
046:
047: import com.quadcap.util.Debug;
048:
049: /**
050: * Used in conjunction with a <code>GroupByCursor</code> to handle
051: * aggregate functions (e.g., <b>SUM</b>, <b>AVG</b>, etc.) with
052: * a <b>GROUP BY</b> clause.
053: *
054: * @author Stan Bailes
055: */
056: public class AggregateCursor extends FilterCursor {
057: GroupByCursor gcursor = null;
058: Vector aggregates = null;
059: Row row = null;
060: int currentRowNum = 0;
061: boolean first = true;
062: boolean isItemCursor = false;
063: ItemsCursor itemsCursor = null;
064: Cursor baseCursor = null;
065:
066: public AggregateCursor(Session session, Cursor cursor,
067: GroupByCursor gcursor, Vector aggregates)
068: throws SQLException {
069: super (session, cursor);
070: isItemCursor = (cursor instanceof ItemsCursor);
071: if (isItemCursor) {
072: itemsCursor = (ItemsCursor) cursor;
073: baseCursor = itemsCursor.getBaseCursor();
074: } else {
075: baseCursor = cursor;
076: }
077: this .gcursor = gcursor;
078: this .aggregates = aggregates;
079: }
080:
081: public void resetAggregates() throws SQLException {
082: if (aggregates != null) {
083: for (int i = 0; i < aggregates.size(); i++) {
084: try {
085: ((AggregateExpression) aggregates.elementAt(i))
086: .reset(session);
087: } catch (IOException e) {
088: throw DbException.wrapThrowable(e);
089: }
090: }
091: }
092: }
093:
094: public void updateAggregates(Cursor c) throws SQLException {
095: if (aggregates != null) {
096: for (int i = 0; i < aggregates.size(); i++) {
097: AggregateExpression ae = (AggregateExpression) aggregates
098: .elementAt(i);
099: ae.updateAggregate(session, c);
100: }
101: }
102: }
103:
104: public Row getRow() throws SQLException {
105: return row;
106: }
107:
108: public void updateRow(Row row) throws SQLException {
109: throw new SQLException(
110: "Aggregate expressions aren't updateable", "42000");
111: }
112:
113: public void deleteRow() throws SQLException {
114: throw new SQLException(
115: "Aggregate expressions aren't updateable", "42000");
116: }
117:
118: public void beforeFirst() throws SQLException {
119: cursor.beforeFirst();
120: first = true;
121: }
122:
123: /**
124: * This routine returns the next element of an aggregate cursor,
125: * i.e., one which uses SUM, COUNT, AVG, MAX, or MIN.
126: *
127: * <p>
128: * If GROUP BY is not specified, 'next()' simply fetches all of
129: * the underlying rows, updating the aggregate expressions after
130: * each row. If there is a GROUP BY clause, we have to keep track
131: * of when a new group starts using our associated group-by cursor.
132: */
133: public boolean next() throws SQLException {
134: boolean any = false;
135: boolean ret = first;
136: first = false;
137: resetAggregates();
138: while (cursor.next()) {
139: updateAggregates(baseCursor);
140: ret = true;
141: if (gcursor != null && gcursor.lastRowOfGroup()) {
142: any = true;
143: break;
144: }
145: }
146: if (ret) {
147: if (isItemCursor) {
148: if (any) {
149: row = cursor.getRow();
150: if (row == null) {
151: row = itemsCursor.getEmptyAggregate();
152: }
153: } else if (gcursor == null) {
154: row = itemsCursor.getEmptyAggregate();
155: } else {
156: ret = false;
157: }
158: } else {
159: ret = false;
160: }
161: }
162: return ret;
163: }
164:
165: public boolean isWritable(int col) throws SQLException {
166: return false;
167: }
168:
169: /**
170: * We don't know the size.
171: */
172: public long size() {
173: return -1;
174: }
175:
176: public void close() throws SQLException {
177: resetAggregates();
178: cursor.close();
179: }
180: }
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