"THROW_ERROR" function does not throw error in vertica_python using python3

[alecsaunders]

The Vertica Error-Handling Function THROW_ERROR does not in fact throw an error on execution when using vertica_python using python3.

Python Version: 3.7.2
Vertica-python version: 0.9.1

When I execute the sql containing the THROW_ERROR function python does NOT throw an error.

cur.execute("SELECT THROW_ERROR('test error')")

It is only when fetchall() or fetchone() is called that an error is thrown.

I have tested this issue by simply calling the function (as shown above) and when using the function inside a case statement:

cur.execute("SELECT CASE WHEN COUNT(*) = 10 THEN 'SUCSESS!' ELSE THROW_ERROR('error') END FROM test;

The logic of my script does not require me to return any results with fetchall(). I would like THROW_ERROR to just throw an error on execution.

---

To provide some help in diagnosing this issue, I noticed that when _execute_simple_query is called in cursor.py, the instance type of self._message (row 479) is RowDescription and not ErrorResponse as it should be. I did some debugging and here is the self._message.

RowDescription: [{'name': 'THROW_ERROR', 'table_oid': 0, 'schema_name': None, 'table_name': None, 'attribute_number': 0, 'data_type_oid': 9, 'data_type_size': 65535, 'data_type_name': 'Varchar', 'null_ok': True, 'is_identity': False, 'type_modifier': 15, 'format_code': 0}]

[sitingren]

@alecsaunders Thanks for reporting. This is a similar issue of #255. Please read the explanation in #255.

Here are protocol messages that are sending(=>) and receiving(<=) during sql executions:

=> Query: SELECT THROW_ERROR('test error');
<= RowDescription: cursor.execute() returned at here
<= ErrorResponse

In vertica-python version 0.9.1, the logic of cursor.execute() makes the function stop reading remaining protocol messages if it receives a RowDescription message. For your specific problem, we can add error handling after receiving RowDescription messages. But in general, ErrorResponse messages can occur anytime in the protocol cycle of a query, only running cursor.fetchall() can you iterate through all remaining protocol messages and catch ErrorResponse.