alamb commented on a change in pull request #9309: URL: https://github.com/apache/arrow/pull/9309#discussion_r565667987
########## File path: rust/datafusion/src/optimizer/boolean_comparison.rs ########## @@ -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 { + #[allow(missing_docs)] + pub fn new() -> Self { + Self {} + } +} + +impl OptimizerRule for BooleanComparison { + fn optimize(&mut self, plan: &LogicalPlan) -> Result<LogicalPlan> { + match plan { + LogicalPlan::Filter { predicate, input } => Ok(LogicalPlan::Filter { + predicate: optimize_expr(predicate), + input: Arc::new(self.optimize(input)?), + }), + // Rest: recurse into plan, apply optimization where possible + LogicalPlan::Projection { .. } + | LogicalPlan::Aggregate { .. } + | LogicalPlan::Limit { .. } + | LogicalPlan::Repartition { .. } + | LogicalPlan::CreateExternalTable { .. } + | LogicalPlan::Extension { .. } + | LogicalPlan::Sort { .. } + | LogicalPlan::Explain { .. } + | LogicalPlan::Join { .. } => { + let expr = utils::expressions(plan); + + // apply the optimization to all inputs of the plan + let inputs = utils::inputs(plan); + let new_inputs = inputs + .iter() + .map(|plan| self.optimize(plan)) + .collect::<Result<Vec<_>>>()?; + + utils::from_plan(plan, &expr, &new_inputs) + } + LogicalPlan::TableScan { .. } | LogicalPlan::EmptyRelation { .. } => { + Ok(plan.clone()) + } + } + } + + fn name(&self) -> &str { + "boolean_comparison" + } +} + +/// Recursively transverses the logical plan. +fn optimize_expr(e: &Expr) -> 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) => right, + Some(false) | None => Expr::Not(Box::new(right)), + }, + (_, Expr::Literal(ScalarValue::Boolean(b))) => match b { + Some(true) => left, + Some(false) | None => Expr::Not(Box::new(left)), + }, + _ => Expr::BinaryExpr { + left: Box::new(left), + op: Operator::Eq, + right: Box::new(right), + }, + }, + Operator::NotEq => match (&left, &right) { + (Expr::Literal(ScalarValue::Boolean(b)), _) => match b { + Some(false) | None => right, + Some(true) => Expr::Not(Box::new(right)), + }, + (_, Expr::Literal(ScalarValue::Boolean(b))) => match b { + Some(false) | None => left, + Some(true) => Expr::Not(Box::new(left)), + }, + _ => Expr::BinaryExpr { + left: Box::new(left), + op: Operator::NotEq, + right: Box::new(right), + }, + }, + _ => Expr::BinaryExpr { + left: Box::new(left), + op: op.clone(), + right: Box::new(right), + }, + } + } + Expr::Not(expr) => Expr::Not(Box::new(optimize_expr(&expr))), + Expr::Case { + expr, + when_then_expr, + else_expr, + } => { + if expr.is_none() { + // recurse into CASE WHEN condition expressions + Expr::Case { + expr: None, + when_then_expr: when_then_expr + .iter() + .map(|(when, then)| (Box::new(optimize_expr(when)), then.clone())) + .collect(), + else_expr: else_expr.clone(), Review comment: That is a good point @houqp -- I think it applies to all expressions (not just CASE statements). You are in essence worried about changing the type of an expression from boolean to something else which is a good thing to worry about! For columns that have types other than boolean, I would expect an expression like `col1 = true` to be eventually rewritten to `CAST(col1, boolean) = true` in which case the optimization to `CAST(col1, boolean)` is correct. Upon reading this code a bit more, I can't recall exactly when cast's (coercions) are inserted. I think skipping the boolean rewrite when `col` is not a boolean is the right thing to do -- and if that type of comparison can happen we need to update the rewrite rules for `BinaryExpr`, `NotExpr`, etc ---------------------------------------------------------------- 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: us...@infra.apache.org
