Support push-down of the filter on coalesce over join keys

Author: vadimpiven

Cargo.lock

@@ -61,6 +61,7 @@ regex-syntax = "0.8.6"
 async-trait = { workspace = true }
 criterion = { workspace = true }
 ctor = { workspace = true }
+datafusion-functions = { workspace = true }
 datafusion-functions-aggregate = { workspace = true }
 datafusion-functions-window = { workspace = true }
 datafusion-functions-window-common = { workspace = true }

datafusion/optimizer/Cargo.toml

@@ -31,7 +31,7 @@ use datafusion_common::{
     assert_eq_or_internal_err, assert_or_internal_err, internal_err, plan_err,
     qualified_name, Column, DFSchema, DataFusionError, Result,
 };
-use datafusion_expr::expr::WindowFunction;
+use datafusion_expr::expr::{Between, InList, ScalarFunction, WindowFunction};
 use datafusion_expr::expr_rewriter::replace_col;
 use datafusion_expr::logical_plan::{Join, JoinType, LogicalPlan, TableScan, Union};
 use datafusion_expr::utils::{
@@ -418,6 +418,204 @@ fn extract_or_clause(expr: &Expr, schema_columns: &HashSet<Column>) -> Option<Ex
     predicate
 }
 
+/// Tracks coalesce predicates that can be pushed to each side of a FULL JOIN.
+struct PushDownCoalesceFilterHelper {
+    join_keys: Vec<(Column, Column)>,
+    left_filters: Vec<Expr>,
+    right_filters: Vec<Expr>,
+    remaining_filters: Vec<Expr>,
+}
+
+impl PushDownCoalesceFilterHelper {
+    fn new(join_keys: &[(Expr, Expr)]) -> Self {
+        let join_keys = join_keys
+            .iter()
+            .filter_map(|(lhs, rhs)| {
+                Some((lhs.try_as_col()?.clone(), rhs.try_as_col()?.clone()))
+            })
+            .collect();
+        Self {
+            join_keys,
+            left_filters: Vec::new(),
+            right_filters: Vec::new(),
+            remaining_filters: Vec::new(),
+        }
+    }
+
+    fn push_columns<F: FnMut(Expr) -> Expr>(
+        &mut self,
+        columns: (Column, Column),
+        mut build_filter: F,
+    ) {
+        self.left_filters
+            .push(build_filter(Expr::Column(columns.0)));
+        self.right_filters
+            .push(build_filter(Expr::Column(columns.1)));
+    }
+
+    fn extract_join_columns(&self, expr: &Expr) -> Option<(Column, Column)> {
+        if let Expr::ScalarFunction(ScalarFunction { func, args }) = expr {
+            if func.name() != "coalesce" {
+                return None;
+            }
+            if let [Expr::Column(lhs), Expr::Column(rhs)] = args.as_slice() {
+                for (join_lhs, join_rhs) in &self.join_keys {
+                    if join_lhs == lhs && join_rhs == rhs {
+                        return Some((lhs.clone(), rhs.clone()));
+                    }
+                    if join_lhs == rhs && join_rhs == lhs {
+                        return Some((rhs.clone(), lhs.clone()));
+                    }
+                }
+            }
+        }
+        None
+    }
+
+    fn push_term(&mut self, term: &Expr) {
+        match term {
+            Expr::BinaryExpr(BinaryExpr { left, op, right })
+                if op.supports_propagation() =>
+            {
+                if let Some(columns) = self.extract_join_columns(left) {
+                    return self.push_columns(columns, |replacement| {
+                        Expr::BinaryExpr(BinaryExpr {
+                            left: Box::new(replacement),
+                            op: *op,
+                            right: right.clone(),
+                        })
+                    });
+                }
+                if let Some(columns) = self.extract_join_columns(right) {
+                    return self.push_columns(columns, |replacement| {
+                        Expr::BinaryExpr(BinaryExpr {
+                            left: left.clone(),
+                            op: *op,
+                            right: Box::new(replacement),
+                        })
+                    });
+                }
+            }
+            Expr::IsNull(expr) => {
+                if let Some(columns) = self.extract_join_columns(expr) {
+                    return self.push_columns(columns, |replacement| {
+                        Expr::IsNull(Box::new(replacement))
+                    });
+                }
+            }
+            Expr::IsNotNull(expr) => {
+                if let Some(columns) = self.extract_join_columns(expr) {
+                    return self.push_columns(columns, |replacement| {
+                        Expr::IsNotNull(Box::new(replacement))
+                    });
+                }
+            }
+            Expr::IsTrue(expr) => {
+                if let Some(columns) = self.extract_join_columns(expr) {
+                    return self.push_columns(columns, |replacement| {
+                        Expr::IsTrue(Box::new(replacement))
+                    });
+                }
+            }
+            Expr::IsFalse(expr) => {
+                if let Some(columns) = self.extract_join_columns(expr) {
+                    return self.push_columns(columns, |replacement| {
+                        Expr::IsFalse(Box::new(replacement))
+                    });
+                }
+            }
+            Expr::IsUnknown(expr) => {
+                if let Some(columns) = self.extract_join_columns(expr) {
+                    return self.push_columns(columns, |replacement| {
+                        Expr::IsUnknown(Box::new(replacement))
+                    });
+                }
+            }
+            Expr::IsNotTrue(expr) => {
+                if let Some(columns) = self.extract_join_columns(expr) {
+                    return self.push_columns(columns, |replacement| {
+                        Expr::IsNotTrue(Box::new(replacement))
+                    });
+                }
+            }
+            Expr::IsNotFalse(expr) => {
+                if let Some(columns) = self.extract_join_columns(expr) {
+                    return self.push_columns(columns, |replacement| {
+                        Expr::IsNotFalse(Box::new(replacement))
+                    });
+                }
+            }
+            Expr::IsNotUnknown(expr) => {
+                if let Some(columns) = self.extract_join_columns(expr) {
+                    return self.push_columns(columns, |replacement| {
+                        Expr::IsNotUnknown(Box::new(replacement))
+                    });
+                }
+            }
+            Expr::Between(between) => {
+                if let Some(columns) = self.extract_join_columns(&between.expr) {
+                    return self.push_columns(columns, |replacement| {
+                        Expr::Between(Between {
+                            expr: Box::new(replacement),
+                            negated: between.negated,
+                            low: between.low.clone(),
+                            high: between.high.clone(),
+                        })
+                    });
+                }
+            }
+            Expr::InList(in_list) => {
+                if let Some(columns) = self.extract_join_columns(&in_list.expr) {
+                    return self.push_columns(columns, |replacement| {
+                        Expr::InList(InList {
+                            expr: Box::new(replacement),
+                            list: in_list.list.clone(),
+                            negated: in_list.negated,
+                        })
+                    });
+                }
+            }
+            _ => {}
+        }
+        self.remaining_filters.push(term.clone());
+    }
+
+    fn push_predicate(
+        mut self,
+        predicate: Expr,
+    ) -> Result<(Option<Expr>, Option<Expr>, Vec<Expr>)> {
+        let predicates = split_conjunction_owned(predicate);
+        let terms = simplify_predicates(predicates)?;
+        for term in terms {
+            self.push_term(&term);
+        }
+        Ok((
+            conjunction(self.left_filters),
+            conjunction(self.right_filters),
+            self.remaining_filters,
+        ))
+    }
+}
+
+fn push_full_join_coalesce_filters(
+    join: &mut Join,
+    predicate: Expr,
+) -> Result<Option<Vec<Expr>>> {
+    let (Some(left), Some(right), remaining) =
+        PushDownCoalesceFilterHelper::new(&join.on).push_predicate(predicate)?
+    else {
+        return Ok(None);
+    };
+
+    let left_input = Arc::clone(&join.left);
+    join.left = Arc::new(make_filter(left, left_input)?);
+
+    let right_input = Arc::clone(&join.right);
+    join.right = Arc::new(make_filter(right, right_input)?);
+
+    Ok(Some(remaining))
+}
+
 /// push down join/cross-join
 fn push_down_all_join(
     predicates: Vec<Expr>,
@@ -527,13 +725,21 @@ fn push_down_all_join(
 }
 
 fn push_down_join(
-    join: Join,
+    mut join: Join,
     parent_predicate: Option<&Expr>,
 ) -> Result<Transformed<LogicalPlan>> {
     // Split the parent predicate into individual conjunctive parts.
-    let predicates = parent_predicate
+    let mut predicates = parent_predicate
         .map_or_else(Vec::new, |pred| split_conjunction_owned(pred.clone()));
 
+    if let Some(parent_predicate) = parent_predicate {
+        if let Some(remaining_predicates) =
+            push_full_join_coalesce_filters(&mut join, parent_predicate.clone())?
+        {
+            predicates = remaining_predicates;
+        }
+    }
+
     // Extract conjunctions from the JOIN's ON filter, if present.
     let on_filters = join
         .filter
@@ -1447,6 +1653,7 @@ mod tests {
     use crate::test::*;
     use crate::OptimizerContext;
     use datafusion_expr::test::function_stub::sum;
+    use datafusion_functions::core::expr_fn::coalesce;
     use insta::assert_snapshot;
 
     use super::*;
@@ -2848,6 +3055,36 @@ mod tests {
         )
     }
 
+    /// Filter on coalesce of join keys should be pushed to both join inputs
+    #[test]
+    fn filter_full_join_on_coalesce() -> Result<()> {
+        let table_scan_t1 = test_table_scan_with_name("t1")?;
+        let table_scan_t2 = test_table_scan_with_name("t2")?;
+
+        let plan = LogicalPlanBuilder::from(table_scan_t1)
+            .join(table_scan_t2, JoinType::Full, (vec!["a"], vec!["a"]), None)?
+            .filter(coalesce(vec![col("t1.a"), col("t2.a")]).eq(lit(1i32)))?
+            .build()?;
+
+        // not part of the test, just good to know:
+        assert_snapshot!(plan,
+        @r"
+        Filter: coalesce(t1.a, t2.a) = Int32(1)
+          Full Join: t1.a = t2.a
+            TableScan: t1
+            TableScan: t2
+        ",
+        );
+        assert_optimized_plan_equal!(
+            plan,
+            @r"
+        Full Join: t1.a = t2.a
+          TableScan: t1, full_filters=[t1.a = Int32(1)]
+          TableScan: t2, full_filters=[t2.a = Int32(1)]
+        "
+        )
+    }
+
     /// join filter should be completely removed after pushdown
     #[test]
     fn join_filter_removed() -> Result<()> {