Fix ambiguous reference when aliasing in combination with ORDER BY

datafusion/optimizer/tests/optimizer_integration.rs

@@ -324,11 +324,10 @@ fn push_down_filter_groupby_expr_contains_alias() {
 fn test_same_name_but_not_ambiguous() {
     let sql = "SELECT t1.col_int32 AS col_int32 FROM test t1 intersect SELECT col_int32 FROM test t2";
     let plan = test_sql(sql).unwrap();
-    let expected = "LeftSemi Join: col_int32 = t2.col_int32\
-    \n  Aggregate: groupBy=[[col_int32]], aggr=[[]]\
-    \n    Projection: t1.col_int32 AS col_int32\
-    \n      SubqueryAlias: t1\
-    \n        TableScan: test projection=[col_int32]\
+    let expected = "LeftSemi Join: t1.col_int32 = t2.col_int32\
+    \n  Aggregate: groupBy=[[t1.col_int32]], aggr=[[]]\
+    \n    SubqueryAlias: t1\
+    \n      TableScan: test projection=[col_int32]\
     \n  SubqueryAlias: t2\
     \n    TableScan: test projection=[col_int32]";
     assert_eq!(expected, format!("{plan:?}"));

datafusion/sql/src/select.rs

@@ -384,7 +384,12 @@ impl<'a, S: ContextProvider> SqlToRel<'a, S> {
                     &[&[plan.schema()]],
                     &plan.using_columns()?,
                 )?;
-                let expr = col.alias(self.normalizer.normalize(alias));
+                let name = self.normalizer.normalize(alias);
+                // avoiding adding an alias if the column name is the same.
+                let expr = match &col {
+                    Expr::Column(column) if column.name.eq(&name) => col,
+                    _ => col.alias(name),
+                };
                 Ok(vec![expr])
             }
             SelectItem::Wildcard(options) => {

datafusion/sql/tests/sql_integration.rs

@@ -3546,13 +3546,24 @@ fn test_select_unsupported_syntax_errors(#[case] sql: &str, #[case] error: &str)
 fn select_order_by_with_cast() {
     let sql =
         "SELECT first_name AS first_name FROM (SELECT first_name AS first_name FROM person) ORDER BY CAST(first_name as INT)";
-    let expected = "Sort: CAST(first_name AS first_name AS Int32) ASC NULLS LAST\
-                        \n  Projection: first_name AS first_name\
-                        \n    Projection: person.first_name AS first_name\
+    let expected = "Sort: CAST(person.first_name AS Int32) ASC NULLS LAST\
+                        \n  Projection: person.first_name\
+                        \n    Projection: person.first_name\
                         \n      TableScan: person";
     quick_test(sql, expected);
 }
 
+#[test]
+fn test_avoid_add_alias() {
+    // avoiding adding an alias if the column name is the same.
+    // plan1 = plan2
+    let sql = "select person.id as id from person order by person.id";
+    let plan1 = logical_plan(sql).unwrap();
+    let sql = "select id from person order by id";
+    let plan2 = logical_plan(sql).unwrap();
+    assert_eq!(format!("{plan1:?}"), format!("{plan2:?}"));
+}
+
 #[test]
 fn test_duplicated_left_join_key_inner_join() {
     //  person.id * 2 happen twice in left side.

datafusion/sqllogictest/test_files/select.slt

@@ -868,6 +868,21 @@ statement error DataFusion error: Error during planning: EXCLUDE or EXCEPT conta
 SELECT * EXCLUDE(d, b, c, a, a, b, c, d)
 FROM table1
 
+# avoiding adding an alias if the column name is the same
+query TT
+EXPLAIN select a as a FROM table1 order by a
+----
+logical_plan
+Sort: table1.a ASC NULLS LAST
+--TableScan: table1 projection=[a]
+physical_plan
+SortExec: expr=[a@0 ASC NULLS LAST]
+--MemoryExec: partitions=1, partition_sizes=[1]
+
+# ambiguous column references in on join
+query error DataFusion error: Schema error: Ambiguous reference to unqualified field a
+EXPLAIN select a as a FROM table1 t1 CROSS JOIN table1 t2 order by a
+
 # run below query in multi partitions
 statement ok
 set datafusion.execution.target_partitions = 2;