@tool
def sql_engine(query: str) -> str:
    """
    Executes an SQL SELECT query and returns the results.

    Parameters:
        query (str): The SQL query string to execute. Only SELECT queries are allowed.

    Returns:
        str: A formatted string containing the query results, or an error message if the query fails.
    """
    try:
        with engine.connect() as con:
            rows = con.execute(text(query)).fetchall()
        if not rows:
            return "No results found."
        return "\n".join([", ".join(map(str, row)) for row in rows])
    except Exception as e:
        return f"Error: {str(e)}"