CREATE TABLE Subjects (subject_id NUMBER, subject_name VARCHAR2)
CREATE TABLE Course_Authors_and_Tutors (author_id NUMBER, author_tutor_ATB VARCHAR2, login_name VARCHAR2, password VARCHAR2, personal_name VARCHAR2, middle_name VARCHAR2, family_name VARCHAR2, gender_mf VARCHAR2, address_line_1 VARCHAR2)
CREATE TABLE Students (student_id NUMBER, date_of_registration DATETIME, date_of_latest_logon DATETIME, login_name VARCHAR2, password VARCHAR2, personal_name VARCHAR2, middle_name VARCHAR2, family_name VARCHAR2)
CREATE TABLE Student_Course_Enrolment (registration_id NUMBER, student_id NUMBER, course_id NUMBER, date_of_enrolment DATETIME, date_of_completion DATETIME)
CREATE TABLE Courses (course_id NUMBER, author_id NUMBER, subject_id NUMBER, course_name VARCHAR2, course_description VARCHAR2)
CREATE TABLE Student_Tests_Taken (registration_id NUMBER, date_test_taken DATETIME, test_result VARCHAR2)

A bar chart for returning the number of the completion date for all the tests that have 'Fail' result, and rank from low to high by the the number of date of completion.
SELECT date_of_completion, COUNT(date_of_completion) FROM Student_Course_Enrolment AS T1 JOIN Student_Tests_Taken AS T2 ON T1.registration_id = T2.registration_id WHERE T2.test_result = "Fail" GROUP BY date_of_completion ORDER BY COUNT(date_of_completion)
SELECT "date_of_completion", COUNT("date_of_completion") FROM "Student_Course_Enrolment" "T1" JOIN "Student_Tests_Taken" "T2" ON "Fail" = "T2"."test_result" AND "T1"."registration_id" = "T2"."registration_id" GROUP BY "date_of_completion" ORDER BY COUNT("date_of_completion")