Pizza究竟有没有复数？

有复数也有单数的,但多数情况下用单数.

牛津高阶英汉双解词典

pizza
/ ˈpiːtsə; ˋpitsə/ n [C, U] Italian dish consisting of a flat (usu round) piece of dough covered with tomatoes, cheese, anchovies, etc and baked in an oven 意大利饼（饼上覆蕃茄、 奶酪、 鯷等, 在烤箱中烘制）.

附例句:
a ham and mushroom pizza ◆ Is there any pizza left?

pizza ['pi:tsə]
n. 比萨饼
例句:
Hello, I'd like to order a large cheese pizza, please.
喂，我要订一个（份）大的乳酪比萨。
Let's go pig out on pizza.
让我们出去大吃一顿比萨饼吧！
Pizza dough must be knead for five minutes.
做比萨饼的面团要揉5分钟。

没有

当然有复数，pizza是可数名词，复数加S

1. I have pizzas. I have juice.
我有比萨饼，我有果汁。

2. Did you ever have pizzas before?
你从前吃过意大利馅饼？