Selecting arbitrary value as max - sql

Question

I have two tables, STUDENTS and LOG.
The LOG table may have 0 or more records in it per student. The records in the LOG table are categorized by column SUBTYPE. Values for SUBTYPE are: 'H', 'L1', 'L2', 'L3', 'M', 'P1', 'P2', and 'Px'.
I am trying to produce a report that will list each student name one time, and the most severe of the codes in the LOG table.
I naturally think of MAX(subtype), but that won't work because I'm not trying to select the actual maximum alphanumeric value of the subtypes - I'm trying to select based on a pre-defined "SEVERITY". Severity, BTW, is not stored in the DB, so I need to define this somehow inside of the query.
For Example...
STUDENTS TABLE
ID LAST_NAME FIRST_NAME
------------------------------------
2 Smith John
3 Jones Bob
4 Bower Jack
LOG TABLE
ID STUDENTSID SUBTYPE
------------------------------------
1 2 P1
2 2 M
3 2 L1
4 3 L2
5 3 P2
6 3 H
The subtype values should actually be ranked/sorted as:
(From Least Severe)
1. P1
2. L1
3. M
4. L2
5. P2
6. H
7. L3
8. Px
(To Most Severe)
Below is what I need my report to look like. Note, Jack Bower is not on the report, as he does not have any records in the log table.
DESIRED REPORT OUTPUT:
John Smith --- M
Bob Jones ---- H
Can anybody point me in the right direction?

Answer 1

order by
case subtype
when 'P1' then 1
when 'L1' then 2
when 'M' then 3
...
end

Answer 2

You need to prioritize the subtypes accordingly using row_number function. Then select the first row for each student.
select id,first_name,last_name
from (
select s.*
,row_number() over(partition by s.id
order by case when l.subtype='P1' then 1
when l.subtype='L1' then 2
when l.subtype='M' then 3
when l.subtype='L2' then 4
when l.subtype='P2' then 5
when l.subtype='H' then 6
when l.subtype='L3' then 7
when l.subtype='Px' then 8
end desc) as rnum
from students s
join logs l on s.id=l.studentsid
) x
where rnum = 1