Method f_down

datafusion/optimizer/src/decorrelate.rs:137–174

(&mut self, plan: LogicalPlan)

    type Node = LogicalPlan;

    fn f_down(&mut self, plan: LogicalPlan) -> Result<Transformed<LogicalPlan>> {
        match plan {
            LogicalPlan::Filter(_) => Ok(Transformed::no(plan)),
            // Subquery nodes are scope boundaries for correlation. A nested
            // Subquery's outer references belong to a different decorrelation
            // level and must not be pulled up into the current scope.
            LogicalPlan::Subquery(_) => {
                Ok(Transformed::new(plan, false, TreeNodeRecursion::Jump))
            }
            LogicalPlan::Union(_) | LogicalPlan::Sort(_) | LogicalPlan::Extension(_) => {
                let plan_hold_outer = !plan.all_out_ref_exprs().is_empty();
                if plan_hold_outer {
                    // the unsupported case
                    self.can_pull_up = false;
                    Ok(Transformed::new(plan, false, TreeNodeRecursion::Jump))
                } else {
                    Ok(Transformed::no(plan))
                }
            }
            LogicalPlan::Limit(_) => {
                let plan_hold_outer = !plan.all_out_ref_exprs().is_empty();
                match (self.exists_sub_query, plan_hold_outer) {
                    (false, true) => {
                        // the unsupported case
                        self.can_pull_up = false;
                        Ok(Transformed::new(plan, false, TreeNodeRecursion::Jump))
                    }
                    _ => Ok(Transformed::no(plan)),
                }
            }
            _ if plan.contains_outer_reference() => {
                // the unsupported cases, the plan expressions contain out reference columns(like window expressions)
                self.can_pull_up = false;
                Ok(Transformed::new(plan, false, TreeNodeRecursion::Jump))
            }
            _ => Ok(Transformed::no(plan)),
        }
    }

    fn f_up(&mut self, plan: LogicalPlan) -> Result<Transformed<LogicalPlan>> {
        let subquery_schema = plan.schema();