Why a database query in python works this way?

Why this works:

    cash = db.execute("SELECT cash FROM users WHERE id = :user_id", user_id = session["user_id"])

    # Ensure user can afford the stock
    if cash[0]["cash"] < share * quote["price"]:
        return apology("Not enough money")

and this doesn't:

    cash = db.execute("SELECT cash FROM users WHERE id = :user_id", user_id = session["user_id"])

    # Ensure user can afford the stock
    if cash < share * quote["price"]:
        return apology("Not enough money")

I would like to understand how DB queries work in python. What is that "cash" variable stores? Isn't it the cash value for a user? (int)