feat: Turn of coalescing and fix mutation of join on expressions

crates/polars-mem-engine/src/executors/join.rs

@@ -68,8 +68,8 @@ impl Executor for JoinExec {
             (input_left.execute(state), input_right.execute(state))
         };
 
-        let mut df_left = df_left?;
-        let mut df_right = df_right?;
+        let df_left = df_left?;
+        let df_right = df_right?;
 
         let profile_name = if state.has_node_timer() {
             let by = self
@@ -97,14 +97,6 @@ impl Executor for JoinExec {
                 .map(|e| e.evaluate(&df_right, state))
                 .collect::<PolarsResult<Vec<_>>>()?;
 
-            // make sure that we can join on evaluated expressions
-            for s in &left_on_series {
-                df_left.with_column(s.clone())?;
-            }
-            for s in &right_on_series {
-                df_right.with_column(s.clone())?;
-            }
-
             // prepare the tolerance
             // we must ensure that we use the right units
             #[cfg(feature = "asof_join")]

crates/polars-ops/src/frame/join/args.rs

@@ -35,7 +35,7 @@ impl JoinArgs {
     }
 }
 
-#[derive(Clone, PartialEq, Eq, Debug, Hash, Default)]
+#[derive(Copy, Clone, PartialEq, Eq, Debug, Hash, Default)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub enum JoinCoalesce {
     #[default]
@@ -56,7 +56,7 @@ impl JoinCoalesce {
                 matches!(self, CoalesceColumns)
             },
             #[cfg(feature = "asof_join")]
-            AsOf(_) => false,
+            AsOf(_) => matches!(self, JoinSpecific | CoalesceColumns),
             Cross => false,
             #[cfg(feature = "semi_anti_join")]
             Semi | Anti => false,

crates/polars-ops/src/frame/join/asof/groups.rs

@@ -587,29 +587,36 @@ pub trait AsofJoinBy: IntoDf {
     fn _join_asof_by(
         &self,
         other: &DataFrame,
-        left_on: &str,
-        right_on: &str,
+        left_on: &Series,
+        right_on: &Series,
         left_by: Vec<SmartString>,
         right_by: Vec<SmartString>,
         strategy: AsofStrategy,
         tolerance: Option<AnyValue<'static>>,
         suffix: Option<&str>,
         slice: Option<(i64, usize)>,
+        coalesce: bool,
     ) -> PolarsResult<DataFrame> {
-        let (self_sliced_slot, other_sliced_slot); // Keeps temporaries alive.
-        let (self_df, other_df);
+        let (self_sliced_slot, other_sliced_slot, left_slice_s, right_slice_s); // Keeps temporaries alive.
+        let (self_df, other_df, left_key, right_key);
         if let Some((offset, len)) = slice {
             self_sliced_slot = self.to_df().slice(offset, len);
             other_sliced_slot = other.slice(offset, len);
+            left_slice_s = left_on.slice(offset, len);
+            right_slice_s = right_on.slice(offset, len);
+            left_key = &left_slice_s;
+            right_key = &right_slice_s;
             self_df = &self_sliced_slot;
             other_df = &other_sliced_slot;
         } else {
             self_df = self.to_df();
             other_df = other;
+            left_key = left_on;
+            right_key = right_on;
         }
 
-        let left_asof = self_df.column(left_on)?.to_physical_repr();
-        let right_asof = other_df.column(right_on)?.to_physical_repr();
+        let left_asof = left_key.to_physical_repr();
+        let right_asof = right_key.to_physical_repr();
         let right_asof_name = right_asof.name();
         let left_asof_name = left_asof.name();
         check_asof_columns(
@@ -645,7 +652,7 @@ pub trait AsofJoinBy: IntoDf {
         )?;
 
         let mut drop_these = right_by.get_column_names();
-        if left_asof_name == right_asof_name {
+        if coalesce && left_asof_name == right_asof_name {
             drop_these.push(right_asof_name);
         }
 
@@ -688,8 +695,10 @@ pub trait AsofJoinBy: IntoDf {
         let self_df = self.to_df();
         let left_by = left_by.into_iter().map(|s| s.as_ref().into()).collect();
         let right_by = right_by.into_iter().map(|s| s.as_ref().into()).collect();
+        let left_key = self_df.column(left_on)?;
+        let right_key = other.column(right_on)?;
         self_df._join_asof_by(
-            other, left_on, right_on, left_by, right_by, strategy, tolerance, None, None,
+            other, left_key, right_key, left_by, right_by, strategy, tolerance, None, None, true,
         )
     }
 }

crates/polars-ops/src/frame/join/asof/mod.rs

@@ -208,16 +208,15 @@ pub trait AsofJoin: IntoDf {
     fn _join_asof(
         &self,
         other: &DataFrame,
-        left_on: &str,
-        right_on: &str,
+        left_key: &Series,
+        right_key: &Series,
         strategy: AsofStrategy,
         tolerance: Option<AnyValue<'static>>,
         suffix: Option<String>,
         slice: Option<(i64, usize)>,
+        coalesce: bool,
     ) -> PolarsResult<DataFrame> {
         let self_df = self.to_df();
-        let left_key = self_df.column(left_on)?;
-        let right_key = other.column(right_on)?;
 
         check_asof_columns(left_key, right_key, tolerance.is_some(), true)?;
         let left_key = left_key.to_physical_repr();
@@ -270,8 +269,8 @@ pub trait AsofJoin: IntoDf {
         }?;
 
         // Drop right join column.
-        let other = if left_on == right_on {
-            Cow::Owned(other.drop(right_on)?)
+        let other = if coalesce && left_key.name() == right_key.name() {
+            Cow::Owned(other.drop(right_key.name())?)
         } else {
             Cow::Borrowed(other)
         };
@@ -287,20 +286,6 @@ pub trait AsofJoin: IntoDf {
 
         _finish_join(left, right_df, suffix.as_deref())
     }
-
-    /// This is similar to a left-join except that we match on nearest key rather than equal keys.
-    /// The keys must be sorted to perform an asof join
-    fn join_asof(
-        &self,
-        other: &DataFrame,
-        left_on: &str,
-        right_on: &str,
-        strategy: AsofStrategy,
-        tolerance: Option<AnyValue<'static>>,
-        suffix: Option<String>,
-    ) -> PolarsResult<DataFrame> {
-        self._join_asof(other, left_on, right_on, strategy, tolerance, suffix, None)
-    }
 }
 
 impl AsofJoin for DataFrame {}

crates/polars-ops/src/frame/join/mod.rs

@@ -132,7 +132,7 @@ pub trait DataFrameJoinOps: IntoDf {
             clear(&mut selected_right);
         }
 
-        let should_coalesce = args.coalesce.coalesce(&args.how);
+        let should_coalesce = args.should_coalesce();
         assert_eq!(selected_left.len(), selected_right.len());
 
         #[cfg(feature = "chunked_ids")]
@@ -229,35 +229,32 @@ pub trait DataFrameJoinOps: IntoDf {
                     args.join_nulls,
                 ),
                 #[cfg(feature = "asof_join")]
-                JoinType::AsOf(options) => {
-                    let left_on = selected_left[0].name();
-                    let right_on = selected_right[0].name();
-
-                    match (options.left_by, options.right_by) {
-                        (Some(left_by), Some(right_by)) => left_df._join_asof_by(
-                            other,
-                            left_on,
-                            right_on,
-                            left_by,
-                            right_by,
-                            options.strategy,
-                            options.tolerance,
-                            args.suffix.as_deref(),
-                            args.slice,
-                        ),
-                        (None, None) => left_df._join_asof(
-                            other,
-                            left_on,
-                            right_on,
-                            options.strategy,
-                            options.tolerance,
-                            args.suffix,
-                            args.slice,
-                        ),
-                        _ => {
-                            panic!("expected by arguments on both sides")
-                        },
-                    }
+                JoinType::AsOf(options) => match (options.left_by, options.right_by) {
+                    (Some(left_by), Some(right_by)) => left_df._join_asof_by(
+                        other,
+                        s_left,
+                        s_right,
+                        left_by,
+                        right_by,
+                        options.strategy,
+                        options.tolerance,
+                        args.suffix.as_deref(),
+                        args.slice,
+                        should_coalesce,
+                    ),
+                    (None, None) => left_df._join_asof(
+                        other,
+                        s_left,
+                        s_right,
+                        options.strategy,
+                        options.tolerance,
+                        args.suffix,
+                        args.slice,
+                        should_coalesce,
+                    ),
+                    _ => {
+                        panic!("expected by arguments on both sides")
+                    },
                 },
                 JoinType::Cross => {
                     unreachable!()

crates/polars-plan/src/plans/conversion/dsl_to_ir.rs

@@ -372,15 +372,22 @@ pub fn to_alp_impl(
             input_right,
             left_on,
             right_on,
-            options,
+            mut options,
         } => {
+            let mut turn_off_coalesce = false;
             for e in left_on.iter().chain(right_on.iter()) {
                 if has_expr(e, |e| matches!(e, Expr::Alias(_, _))) {
                     polars_bail!(
                         ComputeError:
                         "'alias' is not allowed in a join key, use 'with_columns' first",
                     )
                 }
+                // Any expression that is not a simple column expression will turn of coalescing.
+                turn_off_coalesce |= has_expr(e, |e| !matches!(e, Expr::Column(_)));
+            }
+            if turn_off_coalesce {
+                let options = Arc::make_mut(&mut options);
+                options.args.coalesce = JoinCoalesce::KeepColumns;
             }
 
             options.args.validation.is_valid_join(&options.args.how)?;

crates/polars-plan/src/plans/optimizer/projection_pushdown/joins.rs

@@ -266,12 +266,18 @@ pub(super) fn process_join(
             );
         }
 
-        // For left and innner joins we can set `coalesce` to `true` if the rhs key columns are not projected.
+        // For left and inner joins we can set `coalesce` to `true` if the rhs key columns are not projected.
         // This saves a materialization.
         if !options.args.should_coalesce()
             && matches!(options.args.how, JoinType::Left | JoinType::Inner)
         {
+            let mut allow_opt = true;
             let non_coalesced_key_is_used = right_on.iter().any(|e| {
+                // Inline expressions other than col should not coalesce.
+                if !matches!(expr_arena.get(e.node()), AExpr::Column(_)) {
+                    allow_opt = false;
+                    return true;
+                }
                 let key_name = e.output_name();
 
                 // If the name is in the lhs table, a suffix is added.
@@ -285,7 +291,7 @@ pub(super) fn process_join(
             });
 
             // If they key is not used, coalesce the columns as that is often cheaper.
-            if !non_coalesced_key_is_used {
+            if !non_coalesced_key_is_used && allow_opt {
                 let options = Arc::make_mut(&mut options);
                 options.args.coalesce = JoinCoalesce::CoalesceColumns;
             }

crates/polars-plan/src/plans/schema.rs

@@ -241,17 +241,18 @@ pub(crate) fn det_join_schema(
     right_on: &[Expr],
     options: &JoinOptions,
 ) -> PolarsResult<SchemaRef> {
-    match options.args.how {
+    match &options.args.how {
         // semi and anti joins are just filtering operations
         // the schema will never change.
         #[cfg(feature = "semi_anti_join")]
         JoinType::Semi | JoinType::Anti => Ok(schema_left.clone()),
-        _ => {
+        _how => {
             let mut new_schema = Schema::with_capacity(schema_left.len() + schema_right.len());
 
             for (name, dtype) in schema_left.iter() {
                 new_schema.with_column(name.clone(), dtype.clone());
             }
+            let should_coalesce = options.args.should_coalesce();
 
             // make sure that expression are assigned to the schema
             // an expression can have an alias, and change a dtype.
@@ -267,13 +268,13 @@ pub(crate) fn det_join_schema(
             // so the columns that are joined on, may have different
             // values so if the right has a different name, it is added to the schema
             #[cfg(feature = "asof_join")]
-            if !options.args.coalesce.coalesce(&options.args.how) {
+            if matches!(_how, JoinType::AsOf(_)) {
                 for (left_on, right_on) in left_on.iter().zip(right_on) {
                     let field_left =
                         left_on.to_field_amortized(schema_left, Context::Default, &mut arena)?;
                     let field_right =
                         right_on.to_field_amortized(schema_right, Context::Default, &mut arena)?;
-                    if field_left.name != field_right.name {
+                    if should_coalesce && field_left.name != field_right.name {
                         if schema_left.contains(&field_right.name) {
                             new_schema.with_column(
                                 _join_suffix_name(&field_right.name, options.args.suffix()).into(),
@@ -292,12 +293,9 @@ pub(crate) fn det_join_schema(
                 join_on_right.insert(field.name);
             }
 
-            let are_coalesced = options.args.coalesce.coalesce(&options.args.how);
-            let is_asof = options.args.how.is_asof();
-
             // Asof joins are special, if the names are equal they will not be coalesced.
             for (name, dtype) in schema_right.iter() {
-                if !join_on_right.contains(name.as_str()) || (!are_coalesced && !is_asof)
+                if !join_on_right.contains(name.as_str()) || (!should_coalesce)
                 // The names that are joined on are merged
                 {
                     if schema_left.contains(name.as_str()) {

py-polars/polars/dataframe/frame.py

@@ -6584,6 +6584,9 @@ def join(
             - True: -> Always coalesce join columns.
             - False: -> Never coalesce join columns.
 
+            Note that joining on any other expressions than `col`
+            will turn off coalescing.
+
         Returns
         -------
         DataFrame

py-polars/polars/lazyframe/frame.py

@@ -3975,6 +3975,9 @@ def join(
             - None: -> join specific.
             - True: -> Always coalesce join columns.
             - False: -> Never coalesce join columns.
+
+            Note that joining on any other expressions than `col`
+            will turn off coalescing.
         allow_parallel
             Allow the physical plan to optionally evaluate the computation of both
             DataFrames up to the join in parallel.

py-polars/tests/unit/datatypes/test_temporal.py

@@ -571,6 +571,7 @@ def test_asof_join_tolerance_grouper() -> None:
         {
             "date": [date(2020, 1, 5), date(2020, 1, 10)],
             "by": [1, 1],
+            "date_right": [date(2020, 1, 5), None],
             "values": [100, None],
         }
     )