Editing Relational calculus (section)

== Example ==
A [[relational algebra]] expression might prescribe the following steps to retrieve the phone numbers and names of book stores that supply ''Some Sample Book'':

# Join book stores and titles over the BookstoreID.
# Restrict the result of that join to tuples for the book ''Some Sample Book''.
# Project the result of that restriction over StoreName and StorePhone.

A relational calculus expression would formulate this query in the following descriptive or declarative manner:

:Get StoreName and StorePhone for book stores such that there exists a title BK with the same BookstoreID value and with a BookTitle value of ''Some Sample Book''.