fix: properly alias with column overlapping name (#16)

sqlframe/base/dataframe.py

@@ -1097,7 +1097,7 @@ def withColumn(self, colName: str, col: Column) -> Self:
         )
         if existing_col_index:
             expression = self.expression.copy()
-            expression.expressions[existing_col_index] = col.expression
+            expression.expressions[existing_col_index] = col.alias(colName).expression
             return self.copy(expression=expression)
         return self.copy().select(col.alias(colName), append=True)
 

tests/unit/standalone/test_dataframe.py

@@ -2,6 +2,7 @@
 
 from sqlglot import expressions as exp
 
+from sqlframe.standalone import functions as F
 from sqlframe.standalone.dataframe import StandaloneDataFrame
 
 pytest_plugins = ["tests.common_fixtures", "tests.unit.standalone.fixtures"]
@@ -44,3 +45,13 @@ def test_persist_storagelevel(standalone_employee: StandaloneDataFrame, compare_
         "SELECT `t31563`.`fname` AS `fname` FROM `t31563` AS `t31563`",
     ]
     compare_sql(df, expected_statements)
+
+
+def test_with_column_duplicate_alias(standalone_employee: StandaloneDataFrame):
+    df = standalone_employee.withColumn("fname", F.col("age").cast("string"))
+    assert df.columns == ["employee_id", "fname", "lname", "age", "store_id"]
+    # Make sure that the new columns is added with an alias to `fname`
+    assert (
+        df.sql(pretty=False)
+        == "SELECT `a1`.`employee_id` AS `employee_id`, CAST(`a1`.`age` AS STRING) AS `fname`, CAST(`a1`.`lname` AS STRING) AS `lname`, `a1`.`age` AS `age`, `a1`.`store_id` AS `store_id` FROM VALUES (1, 'Jack', 'Shephard', 37, 1), (2, 'John', 'Locke', 65, 1), (3, 'Kate', 'Austen', 37, 2), (4, 'Claire', 'Littleton', 27, 2), (5, 'Hugo', 'Reyes', 29, 100) AS `a1`(`employee_id`, `fname`, `lname`, `age`, `store_id`)"
+    )