[4 lines PR] Fix: saving empty query with auto limit crashes

[yoshiokatsuneo]

What type of PR is this?

• Bug Fix

Description

If we save a empty SQL query(like BigQuery, MySQL, postgreSQL) with auto limit(LIMIT 1000) enabled, redash crashes.
This also prevent from running fix_hash (re-creating query_hash) migration.

Redash crashes when saving empty query with auto limit (LIMIT 1000).
This PR fixes the crashing issue.

[2025-05-02 12:58:31,554][PID:22][INFO][werkzeug] 192.168.65.1 - - [02/May/2025 12:58:31] "POST /api/queries/2 HTTP/1.1" 500 -
Traceback (most recent call last):
  File "/usr/local/lib/python3.10/site-packages/flask/app.py", line 2213, in __call__
    return self.wsgi_app(environ, start_response)
  File "/usr/local/lib/python3.10/site-packages/werkzeug/middleware/proxy_fix.py", line 182, in __call__
    return self.app(environ, start_response)
  File "/usr/local/lib/python3.10/site-packages/flask/app.py", line 2193, in wsgi_app
    response = self.handle_exception(e)
  File "/usr/local/lib/python3.10/site-packages/flask_restful/__init__.py", line 298, in error_router
    return original_handler(e)
  File "/usr/local/lib/python3.10/site-packages/flask/app.py", line 2190, in wsgi_app
    response = self.full_dispatch_request()
  File "/usr/local/lib/python3.10/site-packages/flask/app.py", line 1486, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/usr/local/lib/python3.10/site-packages/flask_restful/__init__.py", line 298, in error_router
    return original_handler(e)
  File "/usr/local/lib/python3.10/site-packages/flask/app.py", line 1484, in full_dispatch_request
    rv = self.dispatch_request()
  File "/usr/local/lib/python3.10/site-packages/flask/app.py", line 1469, in dispatch_request
    return self.ensure_sync(self.view_functions[rule.endpoint])(**view_args)
  File "/usr/local/lib/python3.10/site-packages/flask_restful/__init__.py", line 489, in wrapper
    resp = resource(*args, **kwargs)
  File "/usr/local/lib/python3.10/site-packages/flask_login/utils.py", line 277, in decorated_view
    return current_app.ensure_sync(func)(*args, **kwargs)
  File "/usr/local/lib/python3.10/site-packages/flask/views.py", line 109, in view
    return current_app.ensure_sync(self.dispatch_request)(**kwargs)
  File "/app/redash/handlers/base.py", line 31, in dispatch_request
    return super(BaseResource, self).dispatch_request(*args, **kwargs)
  File "/usr/local/lib/python3.10/site-packages/flask_restful/__init__.py", line 604, in dispatch_request
    resp = meth(*args, **kwargs)
  File "/app/redash/permissions.py", line 71, in decorated
    return fn(*args, **kwargs)
  File "/app/redash/handlers/queries.py", line 364, in post
    models.db.session.commit()
  File "/usr/local/lib/python3.10/site-packages/sqlalchemy/orm/scoping.py", line 163, in do
    return getattr(self.registry(), name)(*args, **kwargs)
  File "/usr/local/lib/python3.10/site-packages/sqlalchemy/orm/session.py", line 1046, in commit
    self.transaction.commit()
  File "/usr/local/lib/python3.10/site-packages/sqlalchemy/orm/session.py", line 504, in commit
    self._prepare_impl()
  File "/usr/local/lib/python3.10/site-packages/sqlalchemy/orm/session.py", line 483, in _prepare_impl
    self.session.flush()
  File "/usr/local/lib/python3.10/site-packages/sqlalchemy/orm/session.py", line 2540, in flush
    self._flush(objects)
  File "/usr/local/lib/python3.10/site-packages/sqlalchemy/orm/session.py", line 2681, in _flush
    with util.safe_reraise():
  File "/usr/local/lib/python3.10/site-packages/sqlalchemy/util/langhelpers.py", line 68, in __exit__
    compat.raise_(
  File "/usr/local/lib/python3.10/site-packages/sqlalchemy/util/compat.py", line 182, in raise_
    raise exception
  File "/usr/local/lib/python3.10/site-packages/sqlalchemy/orm/session.py", line 2642, in _flush
    flush_context.execute()
  File "/usr/local/lib/python3.10/site-packages/sqlalchemy/orm/unitofwork.py", line 422, in execute
    rec.execute(self)
  File "/usr/local/lib/python3.10/site-packages/sqlalchemy/orm/unitofwork.py", line 586, in execute
    persistence.save_obj(
  File "/usr/local/lib/python3.10/site-packages/sqlalchemy/orm/persistence.py", line 205, in save_obj
    for (
  File "/usr/local/lib/python3.10/site-packages/sqlalchemy/orm/persistence.py", line 387, in _organize_states_for_save
    mapper.dispatch.before_update(mapper, connection, state)
  File "/usr/local/lib/python3.10/site-packages/sqlalchemy/event/attr.py", line 322, in __call__
    fn(*args, **kw)
  File "/usr/local/lib/python3.10/site-packages/sqlalchemy/orm/events.py", line 731, in wrap
    fn(*arg, **kw)
  File "/app/redash/models/__init__.py", line 847, in receive_before_insert_update
    target.update_query_hash()
  File "/app/redash/models/__init__.py", line 841, in update_query_hash
    self.query_hash = query_runner.gen_query_hash(query_text, should_apply_auto_limit)
  File "/app/redash/query_runner/__init__.py", line 265, in gen_query_hash
    query_text = self.apply_auto_limit(query_text, set_auto_limit)
  File "/app/redash/query_runner/__init__.py", line 325, in apply_auto_limit
    if self.query_is_select_no_limit(last_query):
  File "/app/redash/query_runner/__init__.py", line 291, in query_is_select_no_limit
    parsed_query = sqlparse.parse(query)[0]
IndexError: tuple index out of range

How is this tested?

• Manually

I confirmed that I can just save empty query successfully.

[eradman]

This is a minor edge case, but simple enough!

[eradman]

The other way to

[yoshiokatsuneo]

@eradman Thanks a lot for your review, and marging !!