Question

I have a STUDENT table which contains data about students from a faculty:

STUDENT(ID, Name, Grade, ID_Tutor)

Structure and data:

CREATE TABLE STUDENT
    (`ID` int, `Name` varchar(5), `Grade` int, `ID_Tutor` int);

INSERT INTO STUDENT
    (`ID`, `Name`, `Grade`, `ID_Tutor`)
VALUES
    (1,    'A',     10,       NULL),
    (2,    'B',     9.5,      1),
    (3,    'C',     9,        1),
    (4,    'D',     8,        1),
    (5,    'E',     7,        4),
    (6,    'F',     8,        1),
    (7,    'G',     5,        7),
    (10,   'H',     6,        5)
    (11,   'I',     7,        3),
    (12,   'J',     9,        10),
    (13,   'K',     9.6,      11),
    (14,   'L',     8.9,      5),
    (15,   'M',     9.9,      13),
    (16,   'N',     7,        2),
    (17,   'O',     7.9,      2),
    (18,   'P',     2,        15);

Top 5 faculty grades:

    `ID`, `Name`, `Grade`, `ID_Tutor`
    (1,    'A',     10,       NULL),
    (15,   'M',     9.9,      13),
    (13,   'K',     9.6,      11),
    (2,    'B',     9.5,      1),
    (3,    'C',     9,        1),
    (12,   'J',     9,        10),

In result should appear students with these tutors from the above table.

I want to make a SQL query (MYSQL) to find

• student name,
• tutor name and
• tutor grade

for students whose tutor has a grade in top 5 faculty students (and without using LIMIT and/or ROWNUM – for a Oracle solution).

Result should look like this:

| student name | tutor name | tutor grade |
       'B'           'A'          10           
       'C'           'A'          10           
       'D'           'A'          10           
       'F'           'A'          10           
       'P'           'M'           9.9           
       'M'           'K'           9.6              
       'N'           'B'           9.5            
       'O'           'B'           9.5            
       'I'           'C'           9            

I tried something like this (but not working) and I think I’m complicating a lot… (and I should not use ROWNUM)

SELECT 
    s.ID, 
    s.Name Student, 
    s.Grade, 
    p.ID_Tutor, 
    p.Grade
FROM 
    STUDENT s,
    (SELECT * FROM 
        (SELECT * FROM 
            (SELECT 
                t.Name Tutor , 
                t.ID , 
                Grade Grade_Tutor 
            FROM STUDENT s
                JOIN STUDENT t 
                    on s.ID_Tutor = t.ID
            GROUP BY t.Name, t.ID)
        ORDER BY 3 desc ) 
    WHERE ROWNUM < 6) p
WHERE s.ID_Tutor = p.ID

Give me this error:

    #1248 - Every derived table must have its own alias

Thanks in advance!

Answer 1

Many thanks to @TehShrike, is his answer!!!

The only “downside” is that is using LIMIT, but if someone has a version without LIMIT please post it; until then, thanks again, @TehShrike!

SELECT 
        student.NAME AS student_name, 
        top_five_tutors.NAME AS tutor_name, 
        top_five_tutors.grade AS tutor_grade
FROM (
        SELECT 
                tutor.id, 
                tutor.NAME, 
                tutor.Grade
        FROM (
                SELECT DISTINCT 
                                id_tutor AS id
                FROM student
             ) AS tutor_ids

        JOIN student AS tutor 
            ON tutor.id = tutor_ids.id

        ORDER BY tutor.grade DESC
            LIMIT 5
     ) AS top_five_tutors

JOIN student 
    ON student.id_tutor = top_five_tutors.id