fix: Raise when join projects name with suffix that doesn't exist

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

@@ -41,6 +41,7 @@ pub(super) fn process_asof_join(
     projections_seen: usize,
     lp_arena: &mut Arena<ALogicalPlan>,
     expr_arena: &mut Arena<AExpr>,
+    join_schema: &Schema,
 ) -> PolarsResult<ALogicalPlan> {
     // n = 0 if no projections, so we don't allocate unneeded
     let n = acc_projections.len() * 2;
@@ -152,6 +153,7 @@ pub(super) fn process_asof_join(
                 &mut local_projection,
                 add_local,
                 &options,
+                join_schema,
             );
         }
     }
@@ -198,6 +200,7 @@ pub(super) fn process_join(
     projections_seen: usize,
     lp_arena: &mut Arena<ALogicalPlan>,
     expr_arena: &mut Arena<AExpr>,
+    join_schema: &Schema,
 ) -> PolarsResult<ALogicalPlan> {
     #[cfg(feature = "asof_join")]
     if matches!(options.args.how, JoinType::AsOf(_)) {
@@ -213,6 +216,7 @@ pub(super) fn process_join(
             projections_seen,
             lp_arena,
             expr_arena,
+            join_schema,
         );
     }
 
@@ -299,6 +303,7 @@ pub(super) fn process_join(
                 &mut local_projection,
                 add_local,
                 &options,
+                join_schema,
             );
         }
     }
@@ -345,6 +350,7 @@ fn process_projection(
     local_projection: &mut Vec<ColumnNode>,
     add_local: bool,
     options: &JoinOptions,
+    join_schema: &Schema,
 ) {
     // Path for renamed columns due to the join. The column name of the left table
     // stays as is, the column of the right will have the "_right" suffix.
@@ -373,7 +379,7 @@ fn process_projection(
         let suffix = options.args.suffix();
         // If _right suffix exists we need to push a projection down without this
         // suffix.
-        if leaf_column_name.ends_with(suffix) {
+        if leaf_column_name.ends_with(suffix) && join_schema.contains(leaf_column_name.as_ref()) {
             // downwards name is the name without the _right i.e. "foo".
             let (downwards_name, _) =
                 leaf_column_name.split_at(leaf_column_name.len() - suffix.len());

crates/polars-plan/src/logical_plan/optimizer/projection_pushdown/mod.rs

@@ -567,7 +567,7 @@ impl ProjectionPushDown {
                 left_on,
                 right_on,
                 options,
-                ..
+                schema,
             } => match options.args.how {
                 #[cfg(feature = "semi_anti_join")]
                 JoinType::Semi | JoinType::Anti => process_semi_anti_join(
@@ -595,6 +595,7 @@ impl ProjectionPushDown {
                     projections_seen,
                     lp_arena,
                     expr_arena,
+                    &schema,
                 ),
             },
             HStack {

py-polars/tests/unit/operations/test_join.py

@@ -803,3 +803,15 @@ def test_join_results_in_duplicate_names() -> None:
     rhs = lhs.clone()
     with pytest.raises(pl.DuplicateError, match="'c_right' already exists"):
         lhs.join(rhs, on=["a", "b"], how="left")
+
+
+def test_join_projection_invalid_name_contains_suffix_15243() -> None:
+    df1 = pl.DataFrame({"a": [1, 2, 3]}).lazy()
+    df2 = pl.DataFrame({"a": [1, 2, 3], "b": [4, 5, 6]}).lazy()
+
+    with pytest.raises(pl.ColumnNotFoundError):
+        (
+            df1.join(df2, on="a")
+            .select(pl.col("b").filter(pl.col("b") == pl.col("foo_right")))
+            .collect()
+        )