| /* |
| * 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.drill.exec.physical.impl.scan.project; |
| |
| /** |
| * Core interface for a projected column. Models a column throughout the |
| * projection lifecycle. Columns evolve from unresolved to resolved at |
| * different times. Each class that derives from this interface can act |
| * as a column "node", while declaring its type so it may be processed |
| * easily at the proper type. |
| * <p> |
| * For example, an implicit column is processed at the file schema |
| * resolution phase, converting from unresolved to resolved. At the same |
| * time, table columns remain unresolved, waiting for the table schema |
| * to appear. |
| * <p> |
| * In an advanced, experimental feature, schema persistence sees some |
| * columns transition from resolved to unresolved and back again. |
| * <p> |
| * Having all column nodes derive from this same interface keeps things |
| * tidy. |
| */ |
| |
| public interface ColumnProjection { |
| |
| /** |
| * The name of the column as it appears in the output |
| * row (record batch.) |
| * |
| * @return the output column name |
| */ |
| String name(); |
| } |
