@log_step
def fetch_completed_orders(conn) -> list[tuple]:
    cursor = conn.execute("SELECT * FROM orders WHERE status = 'completed'")
    return cursor.fetchall()

@log_step
def transform_orders(orders: list[dict]) -> list[dict]:
    ...

@log_step
def write_results(conn, rows: list[dict]) -> int:
    conn.execute("CREATE TABLE IF NOT EXISTS orders_transformed "
                 "(order_id, customer_id, amount, status, customer_ltv, spend_tier)")
    conn.executemany(
        "INSERT INTO orders_transformed VALUES (:order_id, :customer_id, :amount, "
        ":status, :customer_ltv, :spend_tier)",
        rows,
    )
    conn.commit()
    return len(rows)