[GitHub] [arrow-datafusion] andygrove commented on a diff in pull request #2421: naive InSubquery implementation

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

andygrove commented on code in PR #2421:
URL: https://github.com/apache/arrow-datafusion/pull/2421#discussion_r863203136


##########
datafusion/core/src/optimizer/subquery_filter_to_join.rs:
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@@ -0,0 +1,312 @@
+// 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 for rewriting subquery filters to joins
+//!
+//! It handles standalone parts of logical conjunction expressions, i.e.
+//! ```text
+//!   WHERE t1.f IN (SELECT f FROM t2) AND t2.f = 'x'
+//! ```
+//! will be rewritten, but
+//! ```text
+//!   WHERE t1.f IN (SELECT f FROM t2) OR t2.f = 'x'
+//! ```
+//! won't
+use std::sync::Arc;
+
+use crate::error::{DataFusionError, Result};
+use crate::execution::context::ExecutionProps;
+use crate::logical_plan::plan::{Filter, Join};
+use crate::logical_plan::{
+    build_join_schema, Expr, JoinConstraint, JoinType, LogicalPlan,
+};
+use crate::optimizer::optimizer::OptimizerRule;
+use crate::optimizer::utils;
+
+/// Optimizer rule for rewriting subquery filters to joins
+#[derive(Default)]
+pub struct SubqueryFilterToJoin {}
+
+impl SubqueryFilterToJoin {
+    #[allow(missing_docs)]
+    pub fn new() -> Self {
+        Self {}
+    }
+}
+
+impl OptimizerRule for SubqueryFilterToJoin {
+    fn optimize(
+        &self,
+        plan: &LogicalPlan,
+        execution_props: &ExecutionProps,
+    ) -> Result<LogicalPlan> {
+        match plan {
+            LogicalPlan::Filter(Filter { predicate, input }) => {
+                // Splitting filter expression into components by AND
+                let mut filters = vec![];
+                utils::split_conjunction(predicate, &mut filters);
+
+                // Searching for subquery-based filters
+                let (subquery_filters, regular_filters): (Vec<&Expr>, Vec<&Expr>) =
+                    filters
+                        .into_iter()
+                        .partition(|&e| matches!(e, Expr::InSubquery { .. }));
+
+                // Check all subquery filters could be rewritten
+                let mut subqueries_in_regular = vec![];
+                regular_filters.iter().try_for_each(|&e| {
+                    extract_subquery_filters(e, &mut subqueries_in_regular)
+                })?;
+
+                if !subqueries_in_regular.is_empty() {
+                    return Err(DataFusionError::NotImplemented(

Review Comment:
   Can we just revert to the original query here rather than fail? 



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