CREATE TABLE Course_Authors_and_Tutors (author_id INT, author_tutor_ATB VARCHAR, login_name VARCHAR, password VARCHAR, personal_name VARCHAR, middle_name VARCHAR, family_name VARCHAR, gender_mf VARCHAR, address_line_1 VARCHAR)
CREATE TABLE Student_Course_Enrolment (registration_id INT, student_id INT, course_id INT, date_of_enrolment DATETIME, date_of_completion DATETIME)
CREATE TABLE Students (student_id INT, date_of_registration DATETIME, date_of_latest_logon DATETIME, login_name VARCHAR, password VARCHAR, personal_name VARCHAR, middle_name VARCHAR, family_name VARCHAR)
CREATE TABLE Student_Tests_Taken (registration_id INT, date_test_taken DATETIME, test_result VARCHAR)
CREATE TABLE Subjects (subject_id INT, subject_name VARCHAR)
CREATE TABLE Courses (course_id INT, author_id INT, subject_id INT, course_name VARCHAR, course_description VARCHAR)

List each test result and its count in descending order of count. Visualize by bar chart.
SELECT test_result, COUNT(*) FROM Student_Tests_Taken GROUP BY test_result ORDER BY COUNT(*) DESC
SELECT "test_result", COUNT(*) FROM "Student_Tests_Taken" GROUP BY "test_result" ORDER BY COUNT(*) DESC NULLS LAST