jonahgao commented on code in PR #9836: URL: https://github.com/apache/arrow-datafusion/pull/9836#discussion_r1543231135
########## datafusion/sql/src/cte.rs: ########## @@ -0,0 +1,212 @@ +// 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. + +use std::sync::Arc; + +use crate::planner::{ContextProvider, PlannerContext, SqlToRel}; + +use arrow::datatypes::Schema; +use datafusion_common::{ + not_impl_err, plan_err, + tree_node::{TreeNode, TreeNodeRecursion}, + Result, +}; +use datafusion_expr::{LogicalPlan, LogicalPlanBuilder, TableSource}; +use sqlparser::ast::{Query, SetExpr, SetOperator, With}; + +impl<'a, S: ContextProvider> SqlToRel<'a, S> { + pub(super) fn plan_with_clause( + &self, + with: With, + planner_context: &mut PlannerContext, + ) -> Result<()> { + let is_recursive = with.recursive; + // Process CTEs from top to bottom + for cte in with.cte_tables { + // A `WITH` block can't use the same name more than once + let cte_name = self.normalizer.normalize(cte.alias.name.clone()); + if planner_context.contains_cte(&cte_name) { + return plan_err!( + "WITH query name {cte_name:?} specified more than once" + ); + } + + // Create a logical plan for the CTE + let cte_plan = if is_recursive { + self.recursive_cte(cte_name.clone(), *cte.query, planner_context)? + } else { + self.non_recursive_cte(*cte.query, planner_context)? + }; + + // Each `WITH` block can change the column names in the last + // projection (e.g. "WITH table(t1, t2) AS SELECT 1, 2"). + let final_plan = self.apply_table_alias(cte_plan, cte.alias)?; + // Export the CTE to the outer query + planner_context.insert_cte(cte_name, final_plan); + } + Ok(()) + } + + fn non_recursive_cte( + &self, + cte_query: Query, + planner_context: &mut PlannerContext, + ) -> Result<LogicalPlan> { + // CTE expr don't need extend outer_query_schema, + // so we clone a new planner_context here. + let mut cte_planner_context = planner_context.clone(); + self.query_to_plan(cte_query, &mut cte_planner_context) + } + + fn recursive_cte( + &self, + cte_name: String, + mut cte_query: Query, + planner_context: &mut PlannerContext, + ) -> Result<LogicalPlan> { + if !self + .context_provider + .options() + .execution + .enable_recursive_ctes + { + return not_impl_err!("Recursive CTEs are not enabled"); + } + + let (left_expr, right_expr, set_quantifier) = match *cte_query.body { + SetExpr::SetOperation { + op: SetOperator::Union, + left, + right, + set_quantifier, + } => (left, right, set_quantifier), + other => { + // If the query is not a UNION, then it is not a recursive CTE + cte_query.body = Box::new(other); + return self.non_recursive_cte(cte_query, planner_context); + } + }; + + // Each recursive CTE consists from two parts in the logical plan: + // 1. A static term (the left hand side on the SQL, where the + // referencing to the same CTE is not allowed) + // + // 2. A recursive term (the right hand side, and the recursive + // part) + + // Since static term does not have any specific properties, it can + // be compiled as if it was a regular expression. This will + // allow us to infer the schema to be used in the recursive term. + + // ---------- Step 1: Compile the static term ------------------ + let static_plan = + self.set_expr_to_plan(*left_expr, &mut planner_context.clone())?; + + // Since the recursive CTEs include a component that references a + // table with its name, like the example below: + // + // WITH RECURSIVE values(n) AS ( + // SELECT 1 as n -- static term + // UNION ALL + // SELECT n + 1 + // FROM values -- self reference + // WHERE n < 100 + // ) + // + // We need a temporary 'relation' to be referenced and used. PostgreSQL + // calls this a 'working table', but it is entirely an implementation + // detail and a 'real' table with that name might not even exist (as + // in the case of DataFusion). + // + // Since we can't simply register a table during planning stage (it is + // an execution problem), we'll use a relation object that preserves the + // schema of the input perfectly and also knows which recursive CTE it is + // bound to. + + // ---------- Step 2: Create a temporary relation ------------------ + // Step 2.1: Create a table source for the temporary relation + let work_table_source = self.context_provider.create_cte_work_table( + &cte_name, + Arc::new(Schema::from(static_plan.schema().as_ref())), + )?; + + // Step 2.2: Create a temporary relation logical plan that will be used + // as the input to the recursive term + let work_table_plan = LogicalPlanBuilder::scan( + cte_name.to_string(), + work_table_source.clone(), + None, + )? + .build()?; + + let name = cte_name.clone(); + + // Step 2.3: Register the temporary relation in the planning context + // For all the self references in the variadic term, we'll replace it + // with the temporary relation we created above by temporarily registering + // it as a CTE. This temporary relation in the planning context will be + // replaced by the actual CTE plan once we're done with the planning. + planner_context.insert_cte(cte_name.clone(), work_table_plan); + + // ---------- Step 3: Compile the recursive term ------------------ + // this uses the named_relation we inserted above to resolve the + // relation. This ensures that the recursive term uses the named relation logical plan + // and thus the 'continuance' physical plan as its input and source + let recursive_plan = + self.set_expr_to_plan(*right_expr, &mut planner_context.clone())?; + + // Check if the recursive term references the CTE itself, Review Comment: Here are the main changes. -- 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. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
