spark MultiInstanceRelation 源码
spark MultiInstanceRelation 代码
文件路径：/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/MultiInstanceRelation.scala
/*
* 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 org.apache.spark.sql.catalyst.analysis
import org.apache.spark.sql.catalyst.plans.logical.LogicalPlan
/**
* A trait that should be mixed into query operators where a single instance might appear multiple
* times in a logical query plan. It is invalid to have multiple copies of the same attribute
* produced by distinct operators in a query tree as this breaks the guarantee that expression
* ids, which are used to differentiate attributes, are unique.
*
* During analysis, operators that include this trait may be asked to produce a new version
* of itself with globally unique expression ids.
*/
trait MultiInstanceRelation {
def newInstance(): LogicalPlan
}
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