Can anyone help me with this SQL code error? - sql

Question

Can anyone help me with this error?
Database info:
CREATE DATABASE School;
Use School to create first table:
CREATE TABLE Classes
(
class_id INT,
name Varchar(45),
dept Char(4),
number CHAR(4),
section Char(2),
location Varchar(45),
meeting_time varchar(45),
PRIMARY KEY(class_id)
);
INSERT INTO Classes
VALUES (000001, 'Intro. to databases', 'info', '1620', '1a', 'sarpy214', 'm/w 1-2:45 pm');
INSERT INTO Classes (class_id, name, dept, number, section, location)
VALUES (000002, 'intro. to sql', 'info', '2630', 'ww', 'online');
INSERT INTO Classes
VALUES (000003, 'Software Engineering I', 'info', '1325', '4c', 'socmahoney205', 't/h 10-11:45 pm');
INSERT INTO Classes (class_id, name, dept, number, section, location)
VALUES (000004, 'Software Engineering II', 'info', '1335', 'ww', 'online');
INSERT INTO Classes
VALUES (000005, 'How to leave the shire & live forever', 'ring', '1001', '1r', 'socmahoney214', 'f 10-11:45 am');
INSERT INTO Classes (class_id, name, dept, number, section, location)
VALUES (000006, 'Living with the demon inside', 'psyc', '1668', 'ww', 'online');
INSERT INTO Classes
VALUES (000007, 'Internet Scripting jedi mastery', 'info', '2430', '2b', 'socmahoney205', 'm/w 10-11:45 am');
UPDATE Classes
SET meeting_time = 't/h 10-11:45 am'
WHERE class_id = 000003;
SELECT * FROM Classes;
Now create 2nd table:
CREATE TABLE Enrol
(
stu_id int,
class_id int,
grade char(1),
PRIMARY KEY (stu_id),
FOREIGN KEY (stu_id) REFERENCES Students(Stu_id),
FOREIGN KEY (class_id) REFERENCES Classes(class_id)
);
INSERT INTO Enrol VALUES (0000001, 000002, 'A');
INSERT INTO Enrol (stu_id, class_id) VALUES (0000002, 000002);
INSERT INTO Enrol VALUES (0000005, 000001, 'D');
INSERT INTO Enrol (stu_id, class_id) VALUES (0000006, 000005);
INSERT INTO Enrol VALUES (0000003, 000006, 'C');
SELECT * FROM Enrol;
Create 3rd table:
CREATE TABLE Students
(
Stu_id INT PRIMARY KEY,
fname VARCHAR(45),
lname VARCHAR(45),
area_code CHAR(3),
phone VARCHAR(8)
);
INSERT INTO Students
VALUES (000001, 'patty', 'melt', '402', '234-9876');
INSERT INTO Students
VALUES (000002, 'bill', 'fold', '402', '531-6222');
INSERT INTO Students
VALUES (000003, 'sam', 'winchester', '402', '234-2346');
INSERT INTO Students
VALUES (000004, 'luke', 'skywalker', '402', '543-1234');
INSERT INTO Students
VALUES (000005, 'charlie', 'kelly', '402', '234-6859');
INSERT INTO Students
VALUES (000006, 'bilbo', 'baggins', '531', '646-3828');
SELECT * FROM Students
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Answer 1

the issue that you used aggregated function and in the group by you need to put all non aggregated function
so add in the group by
GROUP BY S.STU_ID, S.FNAME, S.LNAME;

Answer 2

The "error" is a minor one and several RDBMS will even ignore it.
You see, if you have a tuple such as (ID, FNAME), it is obvious that every ID maps to its own FNAME. It can't be otherwise. So, GROUPing by ID, or grouping by ID and FNAME, is exactly the same thing.
While, on the other hand, in a complex JOIN, you might have different values of a third column from a different table for the same ID value; in that case, you cannot SELECT both ID and this third column when grouping by ID, because the system wouldn't have enough information to decide which, among the possible different values of the third column, should go with each ID. In this case, to solve the quandary you need to add this third column to the GROUP BY, thereby increasing the cardinality of ID in the response: you might now have 1, JOHN SMITH, YELLOW and 1, JOHN SMITH, RED.
Here, your SELECT is of the first kind, but the database engine does not realize or care for this, and insists that you specify a full GROUP with all the fields in the select, even if one is a primary key and the others are in the same table.
So,
GROUP BY S.STU_ID, S.FNAME, S.LNAME