Fix: Only fetchall() when query has RETURNING clause or is SELECT

app/core/database.py

@@ -64,12 +64,18 @@ def execute_query(query: str, params: tuple = None, fetch: bool = True):
             
             # Auto-detect write operations and commit
             query_upper = query.strip().upper()
-            if query_upper.startswith(('INSERT', 'UPDATE', 'DELETE')):
+            is_write = query_upper.startswith(('INSERT', 'UPDATE', 'DELETE'))
+            
+            if is_write:
                 conn.commit()
             
-            if fetch:
+            # Only fetch if there are results to fetch
+            # (SELECT queries or INSERT/UPDATE/DELETE with RETURNING clause)
+            if fetch and (not is_write or 'RETURNING' in query_upper):
                 return cursor.fetchall()
-            return cursor.rowcount
+            elif is_write:
+                return cursor.rowcount
+            return []
     except Exception as e:
         conn.rollback()
         logger.error(f"Query error: {e}")