Query
CREATE TABLE chatbot_user_assignments (
id INTEGER PRIMARY KEY AUTOINCREMENT,
chatbot_id INTEGER NOT NULL,
user_id INTEGER NOT NULL,
assigned_by INTEGER NOT NULL,
assigned_at TEXT NOT NULL,
FOREIGN KEY (chatbot_id) REFERENCES chatbots(id) ON DELETE CASCADE,
FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE,
FOREIGN KEY (assigned_by) REFERENCES users(id),
UNIQUE(chatbot_id, user_id)
)