com.hazelcast.org.apache.calcite.rel.convert.Converter Maven / Gradle / Ivy
/*
* 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.
*/
package com.hazelcast.org.apache.calcite.rel.convert;
import com.hazelcast.org.apache.calcite.plan.RelTraitDef;
import com.hazelcast.org.apache.calcite.plan.RelTraitSet;
import com.hazelcast.org.apache.calcite.rel.RelNode;
import com.hazelcast.org.checkerframework.checker.nullness.qual.Nullable;
/**
* A relational expression implements the interface Converter to
* indicate that it converts a physical attribute, or
* {@link com.hazelcast.org.apache.calcite.plan.RelTrait trait}, of a relational expression
* from one value to another.
*
* Sometimes this conversion is expensive; for example, to convert a
* non-distinct to a distinct object stream, we have to clone every object in
* the input.
*
* A converter does not change the logical expression being evaluated; after
* conversion, the number of rows and the values of those rows will still be the
* same. By declaring itself to be a converter, a relational expression is
* telling the planner about this equivalence, and the planner groups
* expressions which are logically equivalent but have different physical traits
* into groups called RelSets.
*
*
In principle one could devise converters which change multiple traits
* simultaneously (say change the sort-order and the physical location of a
* relational expression). In which case, the method {@link #getInputTraits()}
* would return a {@link com.hazelcast.org.apache.calcite.plan.RelTraitSet}. But for
* simplicity, this class only allows one trait to be converted at a
* time; all other traits are assumed to be preserved.
*/
public interface Converter extends RelNode {
//~ Methods ----------------------------------------------------------------
/**
* Returns the trait of the input relational expression.
*
* @return input trait
*/
RelTraitSet getInputTraits();
/**
* Returns the definition of trait which this converter works on.
*
* The input relational expression (matched by the rule) must possess
* this trait and have the value given by {@link #getInputTraits()}, and the
* traits of the output of this converter given by {@link #getTraitSet()} will
* have one trait altered and the other orthogonal traits will be the same.
*
* @return trait which this converter modifies
*/
@Nullable RelTraitDef getTraitDef();
/**
* Returns the sole input relational expression.
*
* @return child relational expression
*/
RelNode getInput();
}