Question

I have a homework question please help with a little explanation so that I can understand.

You are writing a query, looking for all customers who have never ordered a pepperoni pizza. Which of these queries is the best match?

select distinct 
  c.customer_name 
from 
  customer c, 
  orders o 
where 
  o.customer_id = c.customer_id 
  and o.pizza_type = ‘pepperoni

---

select 
   c.customer_name 
from 
  customer c 
where 
  c.customer_id not in 
  (
     select 
       o.customer_id 
     from 
       orders o 
     where 
       o.pizza_type != ‘pepperoni’
  )

---

select distinct 
  c.customer_name 
from 
  customer c 
  left join orders o 
    on on.customer_id = c.customer_id 
    and o.pizza_type = ‘pepperoni’ 
where 
  o.pizza_type is null

---

select 
  c.customer_name 
from 
  customer c, 
  orders o 
where 
  o.customer_id = c.customer_id 
  and o.pizza_type = ‘pepperoni’ 
group by 
  c.customer_name 
having count(*) = 0

Answer 1

3, assuming that on.customer_id is a typo on your part that should be o.customer_id

Explanation:

1: Selects all customers who have ordered a pepperoni pizza.

2: Selects all customers who have only ever ordered a pepperoni pizza.

3: Selects all customers who have never ordered a pepperoni pizza.

4: Won’t select anyone.