I Want To Add User Id To Invoice/order

Hello, I need to add user ID in invoice/order, can anyone tell me how to do it?

Thank you!

{$order_info.user_id}

Please use this code in the following templates

design/backend/templates/views/orders/details.tpl
design/backend/mail/templates/orders/invoice.tpl

design/themes/THEME/templates/views/orders/details.tpl
design/themes/THEME/mail/templates/orders/invoice.tpl

You sir, are a lifesaver! Thank you!

I think I have a problem, in the Order Details of the shop I can see the ID, but on the e-mail nothing seems to work. In fact no matter what I do on the:

design/themes/THEME/mail/templates/orders/invoice.tpl

seems to make any difference...

On the:

design/backend/mail/templates/orders/invoice.tpl

These changes reflect the email that came to the sales department, is it right?

LE: Clear cache was needed!!! I fix it!!!