/*
// Licensed to Julian Hyde under one or more contributor license
// agreements. See the NOTICE file distributed with this work for
// additional information regarding copyright ownership.
//
// Julian Hyde 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.
*/
package org.eigenbase.rel;

import org.eigenbase.relopt.*;

/**
 * Definition of the ordering trait.
 *
 * <p>Ordering is a physical property (i.e. a trait) because it can be changed
 * without loss of information. The converter to do this is the {@link SortRel}
 * operator.</p>
 *
 * <p>Unlike other current traits, a {@link RelNode} can have more than one
 * value of this trait simultaneously. For example,
 * <code>TableAccessRel(table=TIME_BY_DAY)</code> might be sorted by
 * <code>{the_year, the_month, the_date}</code> and also by
 * <code>{time_id}</code>. We have to allow a RelNode to belong to more than
 * one RelSubset (these RelSubsets are always in the same set).</p>
 */
public class RelCollationTraitDef extends RelTraitDef<RelCollation>
{
    public static final RelCollationTraitDef INSTANCE =
        new RelCollationTraitDef();

    private RelCollationTraitDef() {
    }

    public Class<RelCollation> getTraitClass() {
        return RelCollation.class;
    }

    public String getSimpleName() {
        return "sort";
    }

    @Override
    public boolean multiple() {
        return true;
    }

    public RelCollation getDefault() {
        return RelCollationImpl.EMPTY;
    }

    public RelNode convert(
        RelOptPlanner planner,
        RelNode rel,
        RelCollation toCollation,
        boolean allowInfiniteCostConverters)
    {
        return new SortRel(
            rel.getCluster(),
            rel.getTraitSet().plus(toCollation),
            rel,
            toCollation);
    }

    public boolean canConvert(
        RelOptPlanner planner, RelCollation fromTrait, RelCollation toTrait)
    {
        return true;
    }
}

// End RelCollationTraitDef.java

Make sortedness a trait, and add a rule, RemoveSortRule, that implements ORDER BY by finding a rel that is already sorted. SortRel is now defined by a RelCollation, not a List<RelFieldCollation>, although they are fairly similar in content. (Most of the functionality is disabled in this commit.)
Make sortedness a trait, and add a rule, RemoveSortRule, that implements ORDER BY by finding a rel that is already sorted. SortRel is now defined by a RelCollation, not a List<RelFieldCollation>, although they are fairly similar in content. (Most of the functionality is disabled in this commit.)
