CS145 - Stanford - Relational Algebra Exercise

Relational Algebra Reference Guide: http://www.db-class.org/course/resources/index?page=ra
Databases in Use: http://www.db-class.org/course/resources/index?page=pizzadata


1. Find all pizzas eaten by at least one female over the age of 20.

\project_{pizza} (
   (\project_{name}
      \select_{gender='female' and age > 20}
      Person
   )
   \join Eats
)

2. Find the names of all females who eat at least one pizza served by Straw Hat. (Note: The pizza need not be eaten at Straw Hat.)

\project_{name}(
   (\project_{name}
      \select_{gender='female'}
         Person
   )
   \join
      (
         ( Eats)
            \join
            ( \select_{pizzeria='Straw Hat'} Serves)
      )
)

3. Find all pizzerias that serve at least one pizza for less than $10 that either Amy or Fay (or both) eat.

\project_{pizzeria} (
   ( \select_{price < 10}  Serves )
      \join
   ( \select_{name='Amy' or 'Fay'} Eats )
)

4. Find all pizzerias that serve at least one pizza for less than $10 that both Amy and Fay eat.

\project_{pizzeria} (
   ( \select_{price < 10}  Serves )
      \join
   ( \select_{name='Fay'} Eats )
)

5. Find the names of all people who eat at least one pizza served by Dominos but who do not frequent Dominos.

\project_{name}
   (\select_{pizza='cheese' or pizza='mushroom'} Eats
      \join Person)
      \diff \project_{name}(\select_{pizzeria='Dominos'} Frequents
   \join Person)