How to concatenate two fields from the #__index_users table to show in the dropdown

Dear Sirs,
​
How do I concatenate two fields from the #__index_users table to show in the dropdown?

I currently have in the 'fields to retrieve' field Data16.id Data16.username, and in the dropdown it appears
Data16.username
My 'users' table:

My 'fields to retrieve' field

My returned sql

My front end dropdown

The desired front end drop down

Thank you in advance
​
Mauro

In fields to retrieve:
​

CONCAT(model.field , " - " , model.field2):model.alias

or

CONCAT(field , " - " , field2):alias

Pay attention to the spaces between the commas.

Dear Healyhatman
​
It worked perfectly, you're awesome,
​
Thank you.
​
Mauro