package-info.java

/*
 * 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.
 */

/**
 * Provides a language for representing row-expressions.
 *
 * <h2>Life-cycle</h2>
 *
 * <p>A {@link org.eigenbase.sql2rel.SqlToRelConverter} converts a SQL parse tree
 *     consisting of {@link org.eigenbase.sql.SqlNode} objects into a relational
 *     expression ({@link org.eigenbase.rel.RelNode}). Several kinds of nodes in
 *     this tree have row expressions ({@link org.eigenbase.rex.RexNode}).</p>
 *
 * <p>After the relational expression has been optimized, a
 *     {@link net.hydromatic.optiq.rules.java.JavaRelImplementor} converts it
 *     into to a plan. If the plan is a Java
 *     parse tree, row-expressions are translated into equivalent Java
 *     expressions.</p>
 *
 * <h2>Expressions</h2>
 *
 *
 * <p>Every row-expression has a type. (Compare with
 *     {@link org.eigenbase.sql.SqlNode}, which is created before validation, and
 *     therefore types may not be available.)</p>
 *
 * <p>Every node in the parse tree is a {@link org.eigenbase.rex.RexNode}.
 *     Sub-types are:</p>
 * <ul>
 *     <li>{@link org.eigenbase.rex.RexLiteral} represents a boolean, numeric,
 *         string, or
 *         date constant, or the value <code>NULL</code>.
 *     </li>
 *     <li>{@link org.eigenbase.rex.RexVariable} represents a leaf of the tree. It
 *         has sub-types:
 *         <ul>
 *             <li>{@link org.eigenbase.rex.RexCorrelVariable} is a correlating
 *                 variable for
 *                 nested-loop joins
 *             </li>
 *             <li>{@link org.eigenbase.rex.RexInputRef} refers to a field of an
 *                 input
 *                 relational expression
 *             </li>
 *             <li>{@link org.eigenbase.rex.RexCall} is a call to an operator or
 *                 function.
 *                 By means of special operators, we can use this construct to
 *                 represent
 *                 virtually every non-leaf node in the tree.
 *             </li>
 *             <li>{@link org.eigenbase.rex.RexRangeRef} refers to a collection of
 *                 contiguous fields from an input relational expression. It
 *                 usually exists only
 *                 during translation.
 *             </li>
 *         </ul>
 *     </li>
 * </ul>
 *
 * <p>Expressions are generally
 *     created using a {@link org.eigenbase.rex.RexBuilder} factory.</p>
 *
 * <h2>Related packages</h2>
 * <ul>
 *     <li>{@link org.eigenbase.sql} SQL object model</li>
 *     <li>{@link org.eigenbase.relopt} Core classes, including {@link
 *         org.eigenbase.reltype.RelDataType} and {@link
 *         org.eigenbase.reltype.RelDataTypeFactory}.
 *     </li>
 * </ul>
 */
package org.eigenbase.rex;

// End package-info.java