Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE Project_Staff (role_code VARCHAR, date_from VARCHAR)
### Question:
How many project staff worked as leaders or started working before '1989-04-24 23:51:54'?
### Answer:
SELECT COUNT(*) FROM Project_Staff WHERE role_code = 'leader' OR date_from < '1989-04-24 23:51:54'