fix tests

crates/polars-lazy/src/frame/mod.rs

@@ -1874,7 +1874,7 @@ impl JoinBuilder {
             suffix: self.suffix,
             slice: None,
             join_nulls: self.join_nulls,
-            ..Default::default()
+            coalesce: self.coalesce,
         };
 
         let lp = self

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

@@ -139,6 +139,19 @@ impl Debug for JoinType {
     }
 }
 
+impl JoinType {
+    pub fn is_asof(&self) -> bool {
+        #[cfg(feature = "asof_join")]
+        {
+            matches!(self, JoinType::AsOf(_))
+        }
+        #[cfg(not(feature = "asof_join"))]
+        {
+            false
+        }
+    }
+}
+
 #[derive(Copy, Clone, PartialEq, Eq, Default, Hash)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 pub enum JoinValidation {

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

@@ -209,9 +209,7 @@ pub trait DataFrameJoinOps: IntoDf {
                 JoinType::Left => {
                     left_df._left_join_from_series(other, s_left, s_right, args, _verbose, None)
                 },
-                JoinType::Outer { .. } => {
-                    left_df._outer_join_from_series(other, s_left, s_right, args)
-                },
+                JoinType::Outer => left_df._outer_join_from_series(other, s_left, s_right, args),
                 #[cfg(feature = "semi_anti_join")]
                 JoinType::Anti => left_df._semi_anti_join_from_series(
                     s_left,
@@ -278,14 +276,14 @@ pub trait DataFrameJoinOps: IntoDf {
             JoinType::Cross => {
                 unreachable!()
             },
-            JoinType::Outer  => {
+            JoinType::Outer => {
                 let names_left = selected_left.iter().map(|s| s.name()).collect::<Vec<_>>();
                 let coalesce = args.coalesce;
                 args.coalesce = JoinCoalesce::KeepColumns;
                 let suffix = args.suffix.clone();
                 let out = left_df._outer_join_from_series(other, &lhs_keys, &rhs_keys, args);
 
-                if matches!(coalesce, JoinCoalesce::CoalesceColumns) {
+                if coalesce.coalesce(&JoinType::Outer) {
                     Ok(_coalesce_outer_join(
                         out?,
                         &names_left,

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

@@ -314,7 +314,7 @@ pub(crate) fn det_join_schema(
                 arena.clear();
             }
             let coalesces_join_keys = options.args.coalesce.coalesce(&options.args.how);
-            // except in asof joins. Asof joins are not equi-joins
+            // Except in asof joins. Asof joins are not equi-joins
             // 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")]
@@ -343,9 +343,12 @@ 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 !coalesces_join_keys || // The names are not merged
-                !join_on_right.contains(name.as_str())
+                if !join_on_right.contains(name.as_str()) || (!are_coalesced && !is_asof)
                 // The names that are joined on are merged
                 {
                     if schema_left.contains(name.as_str()) {