PL/SQL to DECLARE a CURSOR with an EXCEPTION [ERROR] - database

Question

I am using Oracle Apex and I tried various forms of this code but for some reason, I keep getting the same error message and I'm frankly getting frustrated! Can someone please help me and explain why I am getting this wrong? (It's my first advanced dbms course so I hope the question isn't too stupid.)
This is my error:
ORA-06550: line 25, column 16: PLS-00201: identifier 'MARK_ASSG' must be declared
ORA-06512: at "SYS.WWV_DBMS_SQL_APEX_210200", line 673
ORA-06550: line 25, column 1: PL/SQL: Statement ignored
ORA-06550: line 26, column 16: PLS-00201: identifier 'MARK_EXAM' must be declared
ORA-06550: line 26, column 1: PL/SQL: Statement ignored
ORA-06550: line 27, column 11: PLS-00201: identifier 'COEF_ASSG' must be declared
ORA-06550: line 27, column 1: PL/SQL: Statement ignored
ORA-06550: line 28, column 10: PLS-00306: wrong number or types of arguments in call to '+'
ORA-06550: line 28, column 1: PL/SQL: Statement ignored
ORA-06512: at "SYS.DBMS_SYS_SQL", line 1658 ORA-06512: at "SYS.WWV_DBMS_SQL_APEX_210200", line 659 ORA-06512: at "APEX_210200.WWV_FLOW_DYNAMIC_EXEC", line 1829
DECLARE
mark NUMBER(4,1);
nbe INT;
no_student EXCEPTION;
I have the following tables: student, notation, result, course.
Creating table STUDENT and inserting data:
create table student
( nums number(2) primary key, name varchar(20), block number(2) );
insert into student values (10,'A',1);
insert into student values (20,'B',1);
insert into student values (30,'C',1);
insert into student values (40,'D',2);
insert into student values (50,'E',2);
insert into student values (60,'F',3);
Creating table COURSE and inserting data:
create table course
( code_course number(2) primary key, coef_assg number(4, 2), coef_exam number(4, 2) );
insert into course values(1, 0.5, 0.5);
insert into course values(2, 0.2, 0.8);
insert into course values(3, 0.3, 0.7);
insert into course values(4, 0.4, 0.6);
Creating table NOTATION and inserting data:
create table notation
( nums number(2), code_course number(2), mark_assg number(4,1), mark_exam number(4,1),
foreign key (nums) references student(nums),
foreign key (code_course) references course(code_course)
);
insert into notation values(10, 1, 15, 12);
insert into notation values(10, 2, 16, 8);
insert into notation values(10, 3, 12, 13);
insert into notation values(10, 4, 16, 17);
insert into notation values(20, 1, 12, 8);
insert into notation values(20, 2, NULL, 13);
insert into notation values(20, 3, 7, 9);
insert into notation values(20, 4, 17.5, NULL);
insert into notation values(40, 1, 7, 5);
insert into notation values(40, 2, 8, 9);
insert into notation values(40, 3, NULL, 12);
insert into notation values(40, 4, NULL, NULL);
insert into notation values(50, 1, 10, 11.5);
insert into notation values(50, 2, 5, 13);
insert into notation values(50, 3, NULL, 16);
insert into notation values(50, 4, 9, 15);
insert into notation values(60, 1, 15, 12);
insert into notation values(60, 2, 16, 8);
insert into notation values(60, 3, 12 ,13);
insert into notation values(60, 4, 16, 17);
QUESTIONS:
Define a PL/SQL program that enables inserting data in the table RESULT. The calculation of the student final mark must take into account the assignment coefficient (example: 20% = 0.2) and the exam coefficient (example: 80% = 0.8). The student can have a Zero as a mark of an assignment or exam. Thus, use the NVL function to compute the student's final mark in each course.
Define a cursor “student_mark” from tables STUDENT, NOTATION, and COURSE useful to compute the student's final mark in each course.
Define a cursor “student_No_mark” from the table STUDENT to consider the case of the student without marks. Consider the possibility of having no tuple in the STUDENT table. Raise this case as EXCEPTION and insert the values (0, ‘No_student’, NULL, NULL) into the RESULT table.
MY CODE:
DECLARE
mark NUMBER(4,1);
nbe INT;
no_student EXCEPTION;
CURSOR student_mark IS
SELECT student.nums, student.name, course.code_course, course.coef_assg, course.coef_exam, notation.mark_assg, notation.mark_exam
FROM student,course, notation
WHERE (student.nums = notation.nums) AND (notation.code_course=course.code_course);
CURSOR student_no_mark IS
SELECT nums,name
FROM student
WHERE nums NOT IN (SELECT DISTINCT nums FROM notation);
s student_mark%ROWTYPE;
sn student_no_mark%ROWTYPE;
n_mark_assg notation%ROWTYPE;
n_mark_exam notation%ROWTYPE;
n_coef course%ROWTYPE;
BEGIN
DELETE FROM result;
SELECT COUNT(*) INTO nbe FROM student;
IF (nbe=0) THEN RAISE no_student;
END IF;
OPEN student_mark;
FOR s IN student_mark LOOP
n_mark_assg := mark_assg*coef_assg;
n_mark_exam := mark_exam*coef_exam;
n_coef := coef_assg+coef_exam;
mark := (n_mark_assg+n_mark_exam)/(n_coef);
INSERT INTO result VALUES (s.nums, s.name, NULL, 0);
END LOOP;
CLOSE student_mark;
OPEN student_no_mark;
FOR sn IN student_no_mark LOOP
INSERT INTO result VALUES(sn.nums, sn.name, NULL, 0);
END LOOP;
CLOSE student_no_mark;
EXCEPTION
WHEN no_student THEN INSERT INTO result VALUES(0,'No Student', NULL, NULL);
END;

Answer 1

There are a lot of errors in that code. If you solve the errors you are getting now you'll run into other errors. Since this is a learning task, I'm going to point out some issues that are causing the errors and not fix your code. Note that this list might not be exhaustive.
A tip for writing any code: start with the simplest working block, then add a bit of code. If it fails, fix it first, then add a bit more code until you're done. If you write a complete block from the beginning you'll get into an endless loop of fixing errors which could result in code that is a lot worse.
DECLARE
-- tip: prefix local variables with a fixed prefix, eg l_mark instead of mark. It will make your code a lot more readable.
mark NUMBER(4,1);
nbe INT;
no_student EXCEPTION;
-- Tip: use ANSI join syntax
CURSOR student_mark IS
SELECT student.nums, student.name, course.code_course, course.coef_assg, course.coef_exam, notation.mark_assg, notation.mark_exam
FROM student,course, notation
WHERE (student.nums = notation.nums) AND (notation.code_course=course.code_course);
CURSOR student_no_mark IS
SELECT nums,name
FROM student
WHERE nums NOT IN (SELECT DISTINCT nums FROM notation);
-- all the variables below are defined as rowtype. That implies that you have to assign an entire row to them or define the column when assigning.
s student_mark%ROWTYPE;
sn student_no_mark%ROWTYPE;
n_mark_assg notation%ROWTYPE;
n_mark_exam notation%ROWTYPE;
n_coef course%ROWTYPE;
BEGIN
-- there is no ddl for a result table in the question
DELETE FROM result;
SELECT COUNT(*) INTO nbe FROM student;
IF (nbe=0) THEN RAISE no_student;
END IF;
OPEN student_mark;
FOR s IN student_mark LOOP
-- 2 things wrong in row below
-- 1. n_mark_assg is of type ROWTYPE, so you cannot assign a scalar value. Either change datatype of n_mark_assg or assign to a specific column.
-- 2. "mark_assg" and "coeff_assgn" are cursor attributes, reference them with the cursor name (eg s.mark_assg)
n_mark_assg := mark_assg*coef_assg;
n_mark_exam := mark_exam*coef_exam;
n_coef := coef_assg+coef_exam;
mark := (n_mark_assg+n_mark_exam)/(n_coef);
INSERT INTO result VALUES (s.nums, s.name, NULL, 0);
END LOOP;
CLOSE student_mark;
OPEN student_no_mark;
FOR sn IN student_no_mark LOOP
INSERT INTO result VALUES(sn.nums, sn.name, NULL, 0);
END LOOP;
CLOSE student_no_mark;
EXCEPTION
WHEN no_student THEN INSERT INTO result VALUES(0,'No Student', NULL, NULL);
END;
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