wjones127 commented on code in PR #7467: URL: https://github.com/apache/arrow-datafusion/pull/7467#discussion_r1323653945
########## datafusion/optimizer/src/simplify_expressions/guarantees.rs: ########## @@ -0,0 +1,514 @@ +// 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. + +//! Simplifier implementation for [ExprSimplifier::simplify_with_guarantees()][crate::simplify_expressions::expr_simplifier::ExprSimplifier::simplify_with_guarantees]. +use datafusion_common::{tree_node::TreeNodeRewriter, DataFusionError, Result}; +use datafusion_expr::{expr::InList, lit, Between, BinaryExpr, Expr, Operator}; +use std::collections::HashMap; + +use datafusion_physical_expr::intervals::{Interval, IntervalBound, NullableInterval}; + +/// Rewrite expressions to incorporate guarantees. +pub(crate) struct GuaranteeRewriter<'a> { + guarantees: HashMap<&'a Expr, &'a NullableInterval>, +} + +impl<'a> GuaranteeRewriter<'a> { + pub fn new( + guarantees: impl IntoIterator<Item = &'a (Expr, NullableInterval)>, + ) -> Self { + Self { + guarantees: guarantees.into_iter().map(|(k, v)| (k, v)).collect(), + } + } +} + +impl<'a> TreeNodeRewriter for GuaranteeRewriter<'a> { + type N = Expr; + + fn mutate(&mut self, expr: Expr) -> Result<Expr> { + if self.guarantees.is_empty() { + return Ok(expr); + } + + match &expr { + Expr::IsNull(inner) => match self.guarantees.get(inner.as_ref()) { + Some(NullableInterval::Null { .. }) => Ok(lit(true)), + Some(NullableInterval::NotNull { .. }) => Ok(lit(false)), + _ => Ok(expr), + }, + Expr::IsNotNull(inner) => match self.guarantees.get(inner.as_ref()) { + Some(NullableInterval::Null { .. }) => Ok(lit(false)), + Some(NullableInterval::NotNull { .. }) => Ok(lit(true)), + _ => Ok(expr), + }, + Expr::Between(Between { + expr: inner, + negated, + low, + high, + }) => { + if let (Some(interval), Expr::Literal(low), Expr::Literal(high)) = ( + self.guarantees.get(inner.as_ref()), + low.as_ref(), + high.as_ref(), + ) { + let expr_interval = NullableInterval::NotNull { + values: Interval::new( + IntervalBound::new(low.clone(), false), + IntervalBound::new(high.clone(), false), + ), + }; + + let contains = expr_interval.contains(*interval)?; + + if contains.is_certainly_true() { + Ok(lit(!negated)) + } else if contains.is_certainly_false() { + Ok(lit(*negated)) + } else { + Ok(expr) + } + } else { + Ok(expr) + } + } + + Expr::BinaryExpr(BinaryExpr { left, op, right }) => { + // Check if this is a comparison + match op { + Operator::Eq + | Operator::NotEq + | Operator::Lt + | Operator::LtEq + | Operator::Gt + | Operator::GtEq + | Operator::IsDistinctFrom + | Operator::IsNotDistinctFrom => {} + _ => return Ok(expr), + }; + + // Check if this is a comparison between a column and literal + let (col, op, value) = match (left.as_ref(), right.as_ref()) { + (Expr::Column(_), Expr::Literal(value)) => (left, *op, value), + (Expr::Literal(value), Expr::Column(_)) => { + // If we can swap the op, we can simplify the expression + if let Some(op) = op.swap() { + (right, op, value) + } else { + return Ok(expr); + } + } + _ => return Ok(expr), + }; + + if let Some(col_interval) = self.guarantees.get(col.as_ref()) { + let result = col_interval.apply_operator(&op, &value.into())?; + if result.is_certainly_true() { + Ok(lit(true)) + } else if result.is_certainly_false() { + Ok(lit(false)) + } else { + Ok(expr) + } + } else { + Ok(expr) + } + } + + // Columns (if interval is collapsed to a single value) + Expr::Column(_) => { + if let Some(col_interval) = self.guarantees.get(&expr) { + if let Some(value) = col_interval.single_value() { + Ok(lit(value)) + } else { + Ok(expr) + } + } else { + Ok(expr) + } + } + + Expr::InList(InList { + expr: inner, + list, + negated, + }) => { + if let Some(interval) = self.guarantees.get(inner.as_ref()) { + // Can remove items from the list that don't match the guarantee + let new_list: Vec<Expr> = list + .iter() + .filter_map(|expr| { + if let Expr::Literal(item) = expr { + match interval.contains(&NullableInterval::from(item)) { + // If we know for certain the value isn't in the column's interval, + // we can skip checking it. + Ok(NullableInterval::NotNull { values }) + if values == Interval::CERTAINLY_FALSE => + { + None + } + Err(err) => Some(Err(err)), + _ => Some(Ok(expr.clone())), + } + } else { + Some(Ok(expr.clone())) + } + }) + .collect::<Result<_, DataFusionError>>()?; + + Ok(Expr::InList(InList { + expr: inner.clone(), + list: new_list, + negated: *negated, + })) + } else { + Ok(expr) + } + } + + _ => Ok(expr), + } + } +} + +#[cfg(test)] +mod tests { + use super::*; + + use arrow::datatypes::DataType; + use datafusion_common::{tree_node::TreeNode, ScalarValue}; + use datafusion_expr::{col, lit}; + + #[test] + fn test_null_handling() { + // IsNull / IsNotNull can be rewritten to true / false + let guarantees = vec![ + // Note: AlwaysNull case handled by test_column_single_value test, + // since it's a special case of a column with a single value. + ( + col("x"), + NullableInterval::NotNull { + values: Default::default(), + }, + ), + ]; + let mut rewriter = GuaranteeRewriter::new(guarantees.iter()); + + // x IS NULL => guaranteed false + let expr = col("x").is_null(); + let output = expr.clone().rewrite(&mut rewriter).unwrap(); + assert_eq!(output, lit(false)); + + // x IS NOT NULL => guaranteed true + let expr = col("x").is_not_null(); + let output = expr.clone().rewrite(&mut rewriter).unwrap(); + assert_eq!(output, lit(true)); + } + + fn validate_simplified_cases<T>(rewriter: &mut GuaranteeRewriter, cases: &[(Expr, T)]) + where + ScalarValue: From<T>, + T: Clone, + { + for (expr, expected_value) in cases { + let output = expr.clone().rewrite(rewriter).unwrap(); + let expected = lit(ScalarValue::from(expected_value.clone())); + assert_eq!( + output, expected, + "{} simplified to {}, but expected {}", + expr, output, expected + ); + } + } + + fn validate_unchanged_cases(rewriter: &mut GuaranteeRewriter, cases: &[Expr]) { + for expr in cases { + let output = expr.clone().rewrite(rewriter).unwrap(); + assert_eq!( + &output, expr, + "{} was simplified to {}, but expected it to be unchanged", + expr, output + ); + } + } + + #[test] + fn test_inequalities_non_null_bounded() { + let guarantees = vec![ + // x ∈ (1, 3] (not null) + ( + col("x"), + NullableInterval::NotNull { + values: Interval::make(Some(1_i32), Some(3_i32), (true, false)), + }, + ), + ]; + + let mut rewriter = GuaranteeRewriter::new(guarantees.iter()); + + // (original_expr, expected_simplification) + let simplified_cases = &[ + (col("x").lt_eq(lit(1)), false), + (col("x").lt_eq(lit(3)), true), + (col("x").gt(lit(3)), false), + (col("x").gt(lit(1)), true), + (col("x").eq(lit(0)), false), + (col("x").not_eq(lit(0)), true), + (col("x").between(lit(2), lit(5)), true), + (col("x").between(lit(5), lit(10)), false), Review Comment: Good idea. 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