Implement Column expression

rust/datafusion/src/execution/physical_plan/expressions.rs

@@ -0,0 +1,35 @@
+// 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.
+
+//! Defines physical expressions that can evaluated at runtime during query execution
+
+use arrow::array::ArrayRef;
+use arrow::record_batch::RecordBatch;
+use crate::error::Result;
+use crate::execution::physical_plan::PhysicalExpr;
+
+/// Represents the column at a given index in a RecordBatch
+pub struct Column {
+    index: usize
+}
+
+impl PhysicalExpr for Column {
+    /// Evaluate the expression
+    fn evaluate(&self, batch: &RecordBatch) -> Result<ArrayRef> {
+        Ok(batch.column(self.index).clone())
+    }
+}

rust/datafusion/src/execution/physical_plan/mod.rs

@@ -50,4 +50,5 @@ pub trait PhysicalExpr: Send + Sync {
     fn evaluate(&self, batch: &RecordBatch) -> Result<ArrayRef>;
 }
 
+pub mod expressions;
 pub mod projection;