CREATE TABLE student_course_attendance (course_id VARCHAR, student_id VARCHAR)
CREATE TABLE courses (course_id VARCHAR)

How many courses do the student whose id is 171 attend?
SELECT COUNT(*) FROM courses AS T1 JOIN student_course_attendance AS T2 ON T1.course_id = T2.course_id WHERE T2.student_id = 171
SELECT COUNT(*) FROM "courses" AS "T1" JOIN "student_course_attendance" AS "T2" ON "T1"."course_id" = "T2"."course_id" AND "T2"."student_id" = 171