Quiero una novia.

Quiero una novia.
 

Why is the article required in the second Spanish sentence?

¿Tienes novia?
Quiero una novia.

In English we would say:

Do you have a girlfriend?
I want a girlfriend.

Why is the article omitted in the first Spanish sentence?

I'm not sure why, but in many cases the noun doesn't require the article when followed by the verb tener. There are some exceptions when the article is needed, but often when the article is added, it's for emphasis. I'm aware of the phenomenon but don't know the rule. Usually in Spanish (because the language is only about 500 years old in writing) there are logical rules for everything.

I remember. Thanks. :)