🐛 Add index column as regular column, too

Closes gh-63.

src/mods4pandas/lib.py

@@ -423,6 +423,9 @@ def insert_into_db_multiple(con, table, ld: List[Dict]):
 def convert_db_to_parquet(con, table, index_col, output_file):
     df = pd.read_sql_query(f"SELECT * FROM {table}", con, index_col)
 
+    # Add index column as regular column, too
+    df[index_col] = df.index
+
     # Convert Python column type into Pandas type
     for c in df.columns:
         column_type = current_columns_types[table][c]