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From tillrohrmann <...@git.apache.org>
Subject [GitHub] flink pull request: [FLINK-2828] [table] Add interfaces for Table ...
Date Sun, 01 Nov 2015 23:57:53 GMT
Github user tillrohrmann commented on a diff in the pull request:

    https://github.com/apache/flink/pull/1237#discussion_r43590351
  
    --- Diff: flink-staging/flink-table/src/main/scala/org/apache/flink/api/table/expressions/analysis/FieldBacktracker.scala
---
    @@ -0,0 +1,75 @@
    +/*
    + * 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.flink.api.table.expressions.analysis
    +
    +import org.apache.flink.api.table.expressions.{Naming, ResolvedFieldReference}
    +import org.apache.flink.api.table.input.{AdaptiveTableSource, TableSource}
    +import org.apache.flink.api.table.plan._
    +
    +object FieldBacktracker {
    +
    +  /**
    +   * Tracks a field back to its Root and returns its original name and AdaptiveTableSource
    +   * if possible.
    +   * This only happens if the field is forwarded unmodified. Renaming operations are
reverted.
    +   *
    +   * @param op start operator
    +   * @param fieldName field name at start operator
    +   * @return original field name with corresponding AdaptiveTableSource or null
    +   */
    +  def resolveFieldNameAndTableSource(op: PlanNode, fieldName: String):
    +      (AdaptiveTableSource, String) = {
    +    op match {
    +      case s@Select(input, selection) =>
    +        var resolvedField: (AdaptiveTableSource, String) = null
    +        // only follow unmodified fields
    +        selection.foreach {
    --- End diff --
    
    But with this implementation you will take the resolved value of the last expression in
`selection`. All other resolved fields will be discarded. Why don't you simply take the first
element of `selection` via `head` and resolve it? Or do you perform any side effects in the
resolve methods?


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