DB Q:

simple answer please.

Modify the recursive query below to define a relation prereq_depth (course_id, prereq_id, depth) where the attribute depth indicates how many levels of intermediate prerequisites are there between the course and the prerequisite. Direct prerequisites have a depth of 0. with recursive c_prereq(course_id, prereq_id) as (select course_id, prereq_id from prereq union select prereq.prereq_id, c prereq.course_id select prereq.coursejd, c_prereq.prereq_id from prereq, c_prereq where prereq.course_id = c_prereq.prereq_id where prereq. prereq_id = c.prereq.course_id) select * from c_prere