CREATE TABLE course (title VARCHAR2, course_id VARCHAR2)
CREATE TABLE prereq (prereq_id VARCHAR2, course_id VARCHAR2)

What is the course title of the prerequisite of course Mobile Computing?
SELECT title FROM course WHERE course_id IN (SELECT T1.prereq_id FROM prereq AS T1 JOIN course AS T2 ON T1.course_id = T2.course_id WHERE T2.title = 'Mobile Computing')
WITH "_u_0" AS (SELECT "T1"."prereq_id" FROM "prereq" "T1" JOIN "course" "T2" ON "T1"."course_id" = "T2"."course_id" AND "T2"."title" = 'Mobile Computing' GROUP BY "prereq_id") SELECT "title" FROM "course" LEFT JOIN "_u_0" "_u_0" ON "_u_0"."" = "course_id" WHERE NOT "_u_0"."" IS NULL