verify flag for user as parameter

I have table users

Userid  flag 
145     1
142     0

a second table Sales

salesId  date        amount
252      01/01/2021  125
23       01/02/2021  300

I need to ckeck each time for user parameter the flag to display or not the data fOr the user 145 I’ll display everything in the table sales because flag=1 but the user 142 I’ll disply nothing beacuse flag =0

CREATE PROCEDURE Sales   (@userID nvarchar(30))
AS
SELECT * FROM sales 
cross join users
WHERE UserID= @userID and flag =1
GO;

The result is incorrect, how to correct it

Answer

Your version would work with select sales.*. However, I would use:

select s.*
from sales s
where exists (select 1
              from users u
              where u.UserId = @UserId and u.flag = 1
             );

This makes it clear that users is just being used for filtering and that there really isn’t a relationship between the two tables (other than the permissioning, of course).