[GitHub] [arrow] Dandandan commented on a change in pull request #9309: ARROW-11366: [Datafusion] support boolean literal in comparison expression

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

Dandandan commented on a change in pull request #9309:
URL: https://github.com/apache/arrow/pull/9309#discussion_r564293129



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File path: rust/datafusion/src/optimizer/boolean_comparison.rs
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@@ -0,0 +1,270 @@
+// 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.
+
+//! Boolean comparision rule rewrites redudant comparison expression involing boolean literal into
+//! unary expression.
+
+use std::sync::Arc;
+
+use crate::error::Result;
+use crate::logical_plan::{Expr, LogicalPlan, Operator};
+use crate::optimizer::optimizer::OptimizerRule;
+use crate::optimizer::utils;
+use crate::scalar::ScalarValue;
+
+/// Optimizer that simplifies comparison expressions involving boolean literals.
+///
+/// Recursively go through all expressionss and simplify the following cases:
+/// * `expr = ture` to `expr`
+/// * `expr = false` to `!expr`
+pub struct BooleanComparison {}
+
+impl BooleanComparison {

Review comment:
       I think we could make this optimizer a bit more generic (not necessary in this PR) to split recursion / pattern match
   
   This is the more "optimizer framework" I had in mind in the comment on the roadmap
   @alamb @jorgecarleitao @vertexclique .
   
   A common strategy (used by Spark) for rule / replacement based  to have a loop that just does something like this:
   
   ```rust
   let changed = False;
   
   while !changed {
       (logical_plan, changed)  = apply_optimizations(rules, logical_plan);
   }
   ```
   
   A rule could be something like (returning `Some` on replaced output) and doesn't need the boilerplate of recursion for every rule.
   
   ```rust
   // Optimizer can work both on expr and logical plans, default returns `None`
   impl OptimizerRule for BooleanComparison {
      fn optimize_expr(&mut self, plan: &Expr) -> Option<Expr> {
          match e {
                Expr::BinaryExpr { left, op, right } => {
               let left = optimize_expr(left);
               let right = optimize_expr(right);
               match op {
                   Operator::Eq => match (&left, &right) {
                       (Expr::Literal(ScalarValue::Boolean(b)), _) => match b {
                           Some(true) => Some(right),
                           Some(false) | None => Some(Expr::Not(Box::new(right))),
                       },
                       (_, Expr::Literal(ScalarValue::Boolean(b))) => match b {
                           Some(true) => Some(left),
                           Some(false) | None => Some(Expr::Not(Box::new(left))),
                       },
                       _ => None,
                   },
                   Operator::NotEq => match (&left, &right) {
                       (Expr::Literal(ScalarValue::Boolean(b)), _) => match b {
                           Some(false) | None => Some(right),
                           Some(true) => Some(Expr::Not(Box::new(right))),
                       },
                       (_, Expr::Literal(ScalarValue::Boolean(b))) => match b {
                           Some(false) | None => left,
                           Some(true) => Some(Expr::Not(Box::new(left))),
                       },
                       _ => None,
                   },
                   _ => None
               }
           }
          }
      }
   }
   
   ```
       




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