Example: The control displays:
Select a color...
The textbox should display 3.
I haven't tested it with SQL Request control, but something like following should work for it as well
I have successfully used Jquery to count selected checkboxes in the same Nintex form. But when I tried to do something similar with a dropdown exposed in the SQL Request control, it did not recognize the selectors I tried, which is all the suggestions in this article: https://stackoverflow.com/questions/3337749/how-do-i-check-how-many-options-there-are-in-a-dropdown-...
have you tried it with sum/length as adviced above?