001    /**
002     * Copyright (c) 2000-present Liferay, Inc. All rights reserved.
003     *
004     * This library is free software; you can redistribute it and/or modify it under
005     * the terms of the GNU Lesser General Public License as published by the Free
006     * Software Foundation; either version 2.1 of the License, or (at your option)
007     * any later version.
008     *
009     * This library is distributed in the hope that it will be useful, but WITHOUT
010     * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
011     * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
012     * details.
013     */
014    
015    package com.liferay.portal.dao.orm.hibernate;
016    
017    import com.liferay.portal.kernel.util.StringBundler;
018    import com.liferay.portal.kernel.util.StringPool;
019    import com.liferay.portal.kernel.util.StringUtil;
020    
021    /**
022     * @author Shepherd Ching
023     * @author Jian Cao
024     * @author Laszlo Csontos
025     */
026    public class DB2Dialect extends org.hibernate.dialect.DB2Dialect {
027    
028            public DB2Dialect() {
029                    registerKeyword("for");
030                    registerKeyword("optimize");
031            }
032    
033            @Override
034            public String getForUpdateString() {
035                    return " for read only with rs use and keep exclusive locks";
036            }
037    
038            @Override
039            public String getLimitString(String sql, int offset, int limit) {
040                    boolean hasOffset = false;
041    
042                    if ((offset > 0) || forceLimitUsage()) {
043                            hasOffset = true;
044                    }
045    
046                    StringBundler sb = null;
047    
048                    if (hasOffset) {
049                            sb = new StringBundler(11);
050                    }
051                    else {
052                            sb = new StringBundler(5);
053                    }
054    
055                    if (!hasOffset) {
056                            addQueryForLimitedRows(sb, sql, limit);
057                            addOptimizeForLimitedRows(sb, limit);
058    
059                            return sb.toString();
060                    }
061    
062                    // Outer query
063    
064                    sb.append("SELECT outerQuery.* FROM (");
065    
066                    // Inner query
067    
068                    sb.append("SELECT innerQuery.*, ");
069                    sb.append("ROW_NUMBER() OVER() AS rowNumber_ FROM (");
070    
071                    addQueryForLimitedRows(sb, sql, limit);
072    
073                    sb.append(") AS innerQuery");
074    
075                    // Offset
076    
077                    sb.append(") AS outerQuery WHERE rowNumber_ > ");
078                    sb.append(offset);
079    
080                    addOptimizeForLimitedRows(sb, limit);
081    
082                    return sb.toString();
083            }
084    
085            @Override
086            public boolean supportsVariableLimit() {
087                    return _SUPPORTS_VARIABLE_LIMIT;
088            }
089    
090            protected void addOptimizeForLimitedRows(StringBundler sb, int limit) {
091                    sb.append(StringPool.SPACE);
092                    sb.append(
093                            StringUtil.replace(
094                                    _SQL_OPTIMIZE_FOR_LIMITED_ROWS, "[$LIMIT$]",
095                                    String.valueOf(limit)));
096            }
097    
098            protected void addQueryForLimitedRows(
099                    StringBundler sb, String sql, int limit) {
100    
101                    sb.append(sql);
102                    sb.append(StringPool.SPACE);
103                    sb.append(
104                            StringUtil.replace(
105                                    _SQL_FETCH_FIRST_LIMITED_ROWS_ONLY, "[$LIMIT$]",
106                                    String.valueOf(limit)));
107            }
108    
109            private static final String _SQL_FETCH_FIRST_LIMITED_ROWS_ONLY =
110                    "FETCH FIRST [$LIMIT$] ROWS ONLY";
111    
112            private static final String _SQL_OPTIMIZE_FOR_LIMITED_ROWS =
113                    "OPTIMIZE FOR [$LIMIT$] ROWS";
114    
115            private static final boolean _SUPPORTS_VARIABLE_LIMIT = false;
116    
117    }