[GitHub] [arrow-datafusion] Dandandan commented on a change in pull request #288: [Datafusion] NOW, CURRENT_TIMESTAMP, CURRENT_TIME functions

[GitBox <gi...@apache.org>]

Dandandan commented on a change in pull request #288:
URL: https://github.com/apache/arrow-datafusion/pull/288#discussion_r628851004



##########
File path: datafusion/src/optimizer/timestamp_evaluation.rs
##########
@@ -0,0 +1,160 @@
+// 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.
+
+//! Optimizer rule to replace timestamp expressions to constants.
+//! This saves time in planning and executing the query.
+use crate::error::Result;
+use crate::logical_plan::{Expr, LogicalPlan};
+use crate::optimizer::optimizer::OptimizerRule;
+
+use super::utils;
+use crate::physical_plan::functions::BuiltinScalarFunction;
+use crate::scalar::ScalarValue;
+use chrono::{DateTime, Utc};
+
+/// Optimization rule that replaces timestamp expressions with their values evaluated
+pub struct TimestampEvaluation {
+    timestamp: DateTime<Utc>,

Review comment:
       I think this is a clever approach, indeed the execution context with optimization can be reused across queries.
   Also, one could disable the optimization rule (or execute an optimixedy plan). The result of the query needs to be correct in those cases too.
   
   My suggestion would be to add a field to the `ExecutionContext` at the start of a query pass it to the optimizers / evaluation code.




-- 
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.

For queries about this service, please contact Infrastructure at:
users@infra.apache.org