SQL Counting Unique Values?

Question

SQL

There is a table orders:
id|user_id
in this table all orders of all users
how to calculate how many unique users user_id in this table?
there is no separate users table, so it is not possible to calculate normally

Answer 1

The query above will return a list of unique values
​​This query will return the count
SELECT COUNT(DISTINCT user_id) FROM orders

Answer 2

Gentlemen, you must be joking.

SELECT userId,COUNT(userId)
FROM orders
GROUP BY userId