From 040224b0aa77244aa33a0cfcd5b2c9d5b11c9bcc Mon Sep 17 00:00:00 2001
From: Andrew Lamb <andrew@nerdnetworks.org>
Date: Sat, 1 Feb 2025 12:14:06 -0500
Subject: [PATCH] Fix join type coercion (#14387)

---
 datafusion/core/tests/dataframe/mod.rs        | 37 ++++++++++++++++++-
 .../optimizer/src/analyzer/type_coercion.rs   | 23 +++++++++---
 2 files changed, 52 insertions(+), 8 deletions(-)

diff --git a/datafusion/core/tests/dataframe/mod.rs b/datafusion/core/tests/dataframe/mod.rs
index 1ebbf92c736e..eed11f634c9d 100644
--- a/datafusion/core/tests/dataframe/mod.rs
+++ b/datafusion/core/tests/dataframe/mod.rs
@@ -30,8 +30,8 @@ use arrow::{
     record_batch::RecordBatch,
 };
 use arrow_array::{
-    Array, BooleanArray, DictionaryArray, Float32Array, Float64Array, Int8Array,
-    UnionArray,
+    record_batch, Array, BooleanArray, DictionaryArray, Float32Array, Float64Array,
+    Int8Array, UnionArray,
 };
 use arrow_buffer::ScalarBuffer;
 use arrow_schema::{ArrowError, SchemaRef, UnionFields, UnionMode};
@@ -1121,6 +1121,39 @@ async fn join() -> Result<()> {
     Ok(())
 }
 
+#[tokio::test]
+async fn join_coercion_unnnamed() -> Result<()> {
+    let ctx = SessionContext::new();
+
+    // Test that join will coerce column types when necessary
+    // even when the relations don't have unique names
+    let left = ctx.read_batch(record_batch!(
+        ("id", Int32, [1, 2, 3]),
+        ("name", Utf8, ["a", "b", "c"])
+    )?)?;
+    let right = ctx.read_batch(record_batch!(
+        ("id", Int32, [10, 3]),
+        ("name", Utf8View, ["d", "c"]) // Utf8View is a different type
+    )?)?;
+    let cols = vec!["name", "id"];
+
+    let filter = None;
+    let join = right.join(left, JoinType::LeftAnti, &cols, &cols, filter)?;
+    let results = join.collect().await?;
+
+    assert_batches_sorted_eq!(
+        [
+            "+----+------+",
+            "| id | name |",
+            "+----+------+",
+            "| 10 | d    |",
+            "+----+------+",
+        ],
+        &results
+    );
+    Ok(())
+}
+
 #[tokio::test]
 async fn join_on() -> Result<()> {
     let left = test_table_with_name("a")
diff --git a/datafusion/optimizer/src/analyzer/type_coercion.rs b/datafusion/optimizer/src/analyzer/type_coercion.rs
index 48a5e2f9a07c..7a41f54c56e1 100644
--- a/datafusion/optimizer/src/analyzer/type_coercion.rs
+++ b/datafusion/optimizer/src/analyzer/type_coercion.rs
@@ -190,7 +190,15 @@ impl<'a> TypeCoercionRewriter<'a> {
             .map(|(lhs, rhs)| {
                 // coerce the arguments as though they were a single binary equality
                 // expression
-                let (lhs, rhs) = self.coerce_binary_op(lhs, Operator::Eq, rhs)?;
+                let left_schema = join.left.schema();
+                let right_schema = join.right.schema();
+                let (lhs, rhs) = self.coerce_binary_op(
+                    lhs,
+                    left_schema,
+                    Operator::Eq,
+                    rhs,
+                    right_schema,
+                )?;
                 Ok((lhs, rhs))
             })
             .collect::<Result<Vec<_>>>()?;
@@ -275,17 +283,19 @@ impl<'a> TypeCoercionRewriter<'a> {
     fn coerce_binary_op(
         &self,
         left: Expr,
+        left_schema: &DFSchema,
         op: Operator,
         right: Expr,
+        right_schema: &DFSchema,
     ) -> Result<(Expr, Expr)> {
         let (left_type, right_type) = get_input_types(
-            &left.get_type(self.schema)?,
+            &left.get_type(left_schema)?,
             &op,
-            &right.get_type(self.schema)?,
+            &right.get_type(right_schema)?,
         )?;
         Ok((
-            left.cast_to(&left_type, self.schema)?,
-            right.cast_to(&right_type, self.schema)?,
+            left.cast_to(&left_type, left_schema)?,
+            right.cast_to(&right_type, right_schema)?,
         ))
     }
 }
@@ -404,7 +414,8 @@ impl TreeNodeRewriter for TypeCoercionRewriter<'_> {
                 ))))
             }
             Expr::BinaryExpr(BinaryExpr { left, op, right }) => {
-                let (left, right) = self.coerce_binary_op(*left, op, *right)?;
+                let (left, right) =
+                    self.coerce_binary_op(*left, self.schema, op, *right, self.schema)?;
                 Ok(Transformed::yes(Expr::BinaryExpr(BinaryExpr::new(
                     Box::new(left),
                     op,