Course: C $($code$,$ name, credits, department$)$

Prerequisite: PR $($code$,$ prerequisite$)$

$4\mathrm{.}3$ Write down the following in SQL

a$)$ Retrieve the prerequisite courses for the "DATABASE" course.

b$)$ Retrieve the courses that require the "DATABASE" course as a prerequisite.

c$)$ Display for each department the list of offered courses that require prerequisites.

d$)$ Display for each department the list of offered courses with no prerequisites.