CREATE TABLE student_course_enrolment (registration_id NUMBER, student_id NUMBER, course_id NUMBER, date_of_enrolment TIME, date_of_completion TIME)
CREATE TABLE students (student_id NUMBER, date_of_registration TIME, date_of_latest_logon TIME, login_name CLOB, password CLOB, personal_name CLOB, middle_name CLOB, family_name CLOB)
CREATE TABLE courses (course_id NUMBER, author_id NUMBER, subject_id NUMBER, course_name CLOB, course_description CLOB)
CREATE TABLE student_tests_taken (registration_id NUMBER, date_test_taken TIME, test_result CLOB)
CREATE TABLE course_authors_and_tutors (author_id NUMBER, author_tutor_atb CLOB, login_name CLOB, password CLOB, personal_name CLOB, middle_name CLOB, family_name CLOB, gender_mf CLOB, address_line_1 CLOB)
CREATE TABLE subjects (subject_id NUMBER, subject_name CLOB)

How many distinct courses are enrolled in by students?
SELECT COUNT(course_id) FROM student_course_enrolment
SELECT COUNT("course_id") FROM "student_course_enrolment"