ORACLE DB query - maximum stipend in faculty - sql

Question

So, i have an task in uni to get max stipend in each faculty from a table with stipends.
Faculty table is:
ID_FACULTY FACULTY_NAME DEAN TELEPHON
---------- ------------------------------ -------------------- --------
10 Informacijas tehnologiju Vitols 63023095
11 Lauksaimniecibas Gaile 63022584
12 Tehniska Dukulis 53020762
13 Partikas tehnologijas Sabovics 63021075
Money table is:
ID_PAYOUT STUDENT_ID PAYOUT_DA STIPEND COMPENSATION
---------- ---------- --------- ---------- ------------
100 1 24-SEP-20 45.25 15
101 7 20-SEP-20 149.99 0
102 3 18-SEP-20 100 0
103 17 02-SEP-20 90.85 20
104 9 03-SEP-20 85 20
105 19 09-SEP-20 70.75 0
106 25 15-SEP-20 55 15
107 17 17-SEP-20 105.54 0
108 15 22-SEP-20 94 0
109 27 28-SEP-20 100 20
And the student table is:
ID_STUDENT SURNAME NAME COURSE_YEAR FACULTY_ID BIRTHDATE
---------- ------------------------- -------------------- ----------- ---------- ---------
1 Lapa Juris 4 13 27-SEP-96
3 Vilkauss Fredis 2 10 17-MAY-99
5 Karlsone Rasa 1 11 13-MAR-00
7 Grozitis Guntars 3 12 16-APR-97
9 Sonciks Jurgis 2 10 17-MAR-99
11 Berzajs Olafs 3 10 14-FEB-97
13 Vike Ilvija 2 13 14-MAY-99
15 Baure Inga 3 11 12-APR-97
17 Viskers Zigmunds 2 13 15-AUG-99
19 Talmanis Harijs 3 13 15-JUL-97
21 Livmanis Indulis 1 10 19-JAN-00
23 Shaveja Uva 2 13 18-FEB-98
25 Lacis Guntis 4 10 17-SEP-96
27 Liepa Guna 4 11 18-AUG-96
29 Klava Juris 2 10 19-MAY-98
I have tried many variations of queries, i think that I even tried all the possible combinations of joins, but i cannot achieve the neccessary result.
One of my queries looked like this:
SQL> SELECT ROW_NUMBER() OVER (ORDER BY surname) "Nr.",
f.faculty_name,
s.surname,
s.name,
MAX(m.stipend)
FROM faculty f, student s INNER JOIN money m ON s.id_student = m.student_id
WHERE s.faculty_id = f.id_faculty
GROUP BY f.faculty_name, s.surname, s.name
ORDER BY s.surname;
Which returned me the following result:
Nr. FACULTY_NAME SURNAME NAME MAX(M.STIPEND)
---------- ------------------------------ ------------------------- -------------------- --------------
1 Lauksaimniecibas Baure Inga 94
2 Tehniska Grozitis Guntars 149.99
3 Informacijas tehnologiju Lacis Guntis 55
4 Partikas tehnologijas Lapa Juris 45.25
5 Lauksaimniecibas Liepa Guna 100
6 Informacijas tehnologiju Sonciks Jurgis 85
7 Partikas tehnologijas Talmanis Harijs 70.75
8 Informacijas tehnologiju Vilkauss Fredis 100
9 Partikas tehnologijas Viskers Zigmunds 105.54
9 rows selected.
So the goal of this task is to retrieve the maximum amount of stipend granted to a student in a certain faculty.
Can someone please tell what am I doing wrong here?

Answer 1

Just max amount per faculty:
SELECT
f.faculty_name,
MAX(m.stipend)
FROM
faculty f
INNER JOIN student s ON s.faculty_id = f.id_faculty
INNER JOIN money m ON s.id_student = m.student_id
GROUP BY f.faculty_name
Max amount and all other details too:
SELECT * FROM
(
SELECT
ROW_NUMBER() OVER (PARTITION BY f.faculty_name ORDER BY m.stipend desc) rn,
f.*,
s.*,
m.*
FROM
faculty f
INNER JOIN student s ON s.faculty_id = f.id_faculty
INNER JOIN money m ON s.id_student = m.student_id
) x
WHERE x.rn = 1
Points of note:
Do not use old style joins; if you ever write one table_name, other_table_name in a FROM block, you're using old style joins. Don't do it; they became bad news about 30 years ago
When you have a max-n-per-group, you specify how finely detailed the group is. If you GROUP BY s.first_name, s.last_name, f.faculty_name then your groups are "every unique combination of firstname/lastname/faculty, so the only way you'll get multiple items in your group is if there are two John Smiths in Mathematics. If the group is to be the whole of mathematics, then the faculty name (and anything else that is uniquely related 1:1 to it, like the faculty ID) is all that you can put in your group. Anything not in a group must be in an aggregation, like MAX
When you want other details too, you either group and max the data and then join this groupmaxed data back to the original data to use it as a filter, or you use an approach like here where you use a row_number or rank, with a partition (which is like an autojoined grouped summary). There is no group here; the row numbering acts like a group because it restarts from 1 every different faculty and proceeds incrementally as stipend decreses. This means that the highest stipend is always in row number 1.
Unlike using a groupmax that you join back to get the detail, the row_number route does not produce duplicate rows with tied-for-highest stipends