Order oracle query result in sequence as of OR clauses - sql

Question

I have an oracle table with structure something like:
School {
Student_Id,
Student_Name,
Class,
Sport,
Club
}
I want to write a query to fetch all students who either belong to X class, or Y Sport, or Z club.
But I want to order the result based on the sequence of my OR conditions.
That is all students belonging to X class will come first, before the students of Y sport. Then students of Z club will come.
Also, no duplicate results. That is if John is from class X & also belongs to sport Y, then he should only be only appear once and on top of all results of sports Y.

Answer 1

This is how I understood the question:
SQL> with school (student_name, class, sport, club) as
2 (select 'Scott', 'x', 'a', 'c' from dual union all
3 select 'Mike' , 'b', 'c', 'z' from dual union all
4 select 'Kate' , 'x', 'y', 'z' from dual union all
5 select 'John' , 'x', 'b', 'd' from dual union all
6 select 'Vito' , 'd', 'e', 'g' from dual
7 )
8 select * from school
9 where class = 'x' or sport = 'y' or club = 'z'
10 order by case when class = 'x' then 1 end,
11 case when sport = 'y' then 2 end,
12 case when club = 'z' then 3 end;
STUDENT CLASS SPORT CLUB
------- ----- ----- -----
Kate x y z
Scott x a c
John x b d
Mike b c z
SQL>
If that's not it, please, post sample data and expected result.

Answer 2

I would write this as:
select s.*
from school s
where class = 'X' or sport = 'Y' or club = 'Z'
order by (case when class = 'X' then 1
when sport = 'Y' then 2
when club = 'Z' then 3
end)
If you don't want to repeat the conditions, you can use a subquery, CTE, or -- in Oracle 12C -- a lateral join:
select s.*
from school s cross join lateral
(select (case when class = 'X' then 1
when sport = 'Y' then 2
when club = 'Z' then 3
end) as ord
from dual
) x
where x.ord is not null
order by x.ord

Answer 3

select student_id
, case when class='X' then 1
when sport = 'Y' then 2
when club='Z' then 3
else 4
end as Ordr
from School
WHERE class='X' or sport = 'Y' or club='Z'
Order by ordr
Explanation:
The WHERE class='X' or sport = 'Y' or club='Z' simply implements your desired filtering.
The custom ordering is implemented by creating an additional column called ordr and using it in the ORDER BY clause. This column is created using a case statement. The order of the how this is written is important because a CASE expression evaluates to the first true condition and, if there is no true condition, it evaluates to the ELSE part.
So all students taking class X will get an ordr of 1, regardless of their sport and club.
If a student does not take class X, the expression will try to evaluate if the student takes sport Y and if that is the case, that student will get assigned an ordr of 2 regardless other column values.
Then if the student does not take either class X nor sport Y, the case expression will check if the student is in club Z. If that is true he will be asigned an ordr of 3.
Lastly, if a student is neither in class X, does sport Y or is in club Z, he wil get assigned an ordr of 4.
ORDER BY is ASCENDING by degfault meaning 1 will show up before 2 and so on.
What this algorithm does not do, which you can tell by the above explanation, is prioritize a student that takes class X, sport Y, club Z over someone that only takes class X.