Convert OuterReferenceColumn to a Column sql node

Author: goldmedal

datafusion/sql/src/unparser/expr.rs

@@ -417,9 +417,7 @@ impl Unparser<'_> {
             Expr::Placeholder(_) => {
                 not_impl_err!("Unsupported Expr conversion: {expr:?}")
             }
-            Expr::OuterReferenceColumn(_, _) => {
-                not_impl_err!("Unsupported Expr conversion: {expr:?}")
-            }
+            Expr::OuterReferenceColumn(_, col) => self.col_to_sql(col),
             Expr::Unnest(_) => not_impl_err!("Unsupported Expr conversion: {expr:?}"),
         }
     }
@@ -874,8 +872,8 @@ mod tests {
     use datafusion_expr::{
         case, col, exists,
         expr::{AggregateFunction, AggregateFunctionDefinition},
-        lit, not, not_exists, table_scan, try_cast, when, wildcard, ColumnarValue,
-        ScalarUDF, ScalarUDFImpl, Signature, Volatility, WindowFrame,
+        lit, not, not_exists, out_ref_col, table_scan, try_cast, when, wildcard,
+        ColumnarValue, ScalarUDF, ScalarUDFImpl, Signature, Volatility, WindowFrame,
         WindowFunctionDefinition,
     };
 
@@ -1160,6 +1158,10 @@ mod tests {
                 try_cast(col("a"), DataType::UInt32),
                 r#"TRY_CAST("a" AS INTEGER UNSIGNED)"#,
             ),
+            (
+                out_ref_col(DataType::Int32, "t.a").gt(lit(1)),
+                r#"("t"."a" > 1)"#,
+            ),
         ];
 
         for (expr, expected) in tests {