How to make a limited number of input of a certain command in aiogram?

Question

Bots

I am writing a bot on aiogram with a link to the PostgreSQL database.

Essence of the question:

There are 2 commands in the bot: ("/start", "/menu")
When you click on /start, the user is added to the PostgreSQL database. (The table looks like: ID, full_name, user_name, telegram_id, quantity). quantity = 10 by default.
When you click on /menu - plain text is displayed.
How to make it so that when you click on / test - quantity decreases each time by 1? Those. 9,8,7... And when quantity became 0, a message was displayed that the limit had been exhausted.

Answer 1

In the /test command handler, do a SELECT quantity for the sender.
If nothing is found, report the need to register via /start.
If a positive value is returned, execute an UPDATE query, and then do what is required.
If zero is returned, report limit exhaustion.
What exactly are the problems?