/*
* #!
* Ontopia Engine
* #-
* Copyright (C) 2001 - 2013 The Ontopia Project
* #-
* Licensed 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 net.ontopia.persistence.query.sql;
/**
* INTERNAL: SQL optimizer that removes A = A and A != A expressions.
*/
public class EqualsSQLOptimizer extends BooleanSQLOptimizer {
// + RULE 1: 'A == A' => true
// + RULE 2: 'A != A' => false
public SQLQuery optimize(SQLQuery query) {
optimizeQuery(query);
return query;
}
protected int optimizeEquals(SQLEquals expr) {
// RULE 1: 'A == A' => true
if (expr.getLeft().equals(expr.getRight())) {
//! System.out.println("Optimizing out: " + expr);
//! optimizeValue(expr.getLeft());
//! optimizeValue(expr.getRight());
return 1;
} else {
return 0;
}
}
protected int optimizeNotEquals(SQLNotEquals expr) {
// RULE 2: 'A != A' => false
if (expr.getLeft().equals(expr.getRight())) {
//! System.out.println("Optimizing out: " + expr);
return -1;
} else {
//! optimizeValue(expr.getLeft());
//! optimizeValue(expr.getRight());
return 0;
}
}
}