Subjunctive question

[Liquinn3]

Hi, why does the first sentence require "que" while the second sentence doesn't require it?

Que tengas un buen fin de semana.
Viva España.

Thanks.

[Rusty]

The second sentence may be said, 'Que viva España', and would mean the same thing. The shortened form (without the leading conjunction) is allowed in some expressions.