Why subjunctive in this sentence? "¿Tiene una que no *tenga* carne?"

Question

In a pizzeria I asked a waiter:

¿Tiene una que no tiene carne?

And he re-asked me:

¿Una que no tenga carne? Hmmmmm.

Why tenga in this case?

Answer 1

It's hypothetical/uncertain if such a pizza exists, which requires subjunctive.

It's easier to see it in another example:

Busco un libro que no tenga dibujos. (Uncertain whether such a book actually exists.).

Now, if you were to say "Busco el libro que no tiene dibujos." your use of the indicative (and the definite article) directly connotes that you know the book exists and you're just trying to find it.

Hope that helps.

Answer 2

To add to ALB's apt answer: The question

¿Tiene una que no tiene carne?

can indeed make sense, but a different sense -probably- than you intended. With it, you'd be asking about the availability of a specific, concrete type of pizza - a type you know it exists; say, one that you already ate there, but you don't remember its name, only that it has not meat.

In contrast, the "right" version

¿Tiene una que no tenga carne?

... or even better

¿Tiene alguna que no tenga carne?

(approximately equivalent: ¿Tiene alguna sin carne?)

... is asking about the availability of some (any) type of pizza (perhaps not existent) that has no meat.

Answer 3

This is referencing the tense where you want to use, if you say:

¿Una que no tenga carne?

Mostly you are referencing in the past tense, because you are talking about when the pizza was made.

Instead when you have this:

¿Una que no tiene carne?

It is talking about something that it is there, if I'm showing you three different pizzas in the desk you can use the second choice, but if you are talking without a reference, I mean in general you should use:

que tenga carne