sql select maximum value record in one to many in sql using joins

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SQL-Server-2008R2

I have 3 tables :-
Table 1 : a (applicant)
Id | Name | DOB
__________________
1 | xyz | 12/01/1990
2 | pqr | 06/02/1995

Table 2: b (Course)
Id | Course
____________
1 | Btech
2 | Mtech
3 | PhD

Table 3 : c
a_Id | b_Id | Year Completed
_______________________________
1 | 1 | 2008
1 | 3 | 2015
1 | 2 | 2012
2 | 2 | 2008
2 | 1 | 2006

I need to retrieve just the highest qualification of both the applicants using joins

Expected Result :
Name | Course | Year Completed
________________________________
xyz | PhD | 2015
pqr | Mtech | 2008

I'm using the below script :

SQL

select *
from a as t1
left outer join 
( select * from C where  Year in  (SELECT MAX(Year) Year FROM C GROUP BY a_Id )) as t2 on t1.Id = t2.a_Id
left outer join b as t3 on t2.b_Id = t3.Id

Posted 18-Aug-15 2:52am

scarletwitch1990

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Wombaticus 18-Aug-15 9:30am

Why are you selecting MAX(year) if you want the highest qualification? I would have thought you'd want MAX(b_Id) in there somewhere.

scarletwitch1990 19-Aug-15 0:47am

@Wombaticus : I do agree that, infact that was my first train of thoughts, but I figured that the Year of completion might be a good parameter to find out the higher qualification.

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CHill60 · Answer 1 · 2015-08-18T03:38:00

Well apart from the fact I get completely different results using the sql you have so far, Wombaticus has raised a perfectly valid point that you shouldn't assume that the higher qualification is gained after the lower qualification.

I would use something like

SQL

with CTE as (
    select Max(b_id) as Highest, a_Id
    from c group by a_Id
)
select a.[Name], b.Course, c.Year_Completed
from CTE
inner join a on a.Id = CTE.a_Id
inner join b on b.Id = CTE.Highest
inner join c on a.Id = c.a_Id and c.b_Id = b.Id

The Common Table Expression determines the highest qualification gained by each applicant. I can then use that to determine the name of the course and link to table c to find the year the applicant gained it. Table a is included only to get the name of the applicant.

Peter Leow · Answer 2 · 2015-08-18T03:39:00

Solution 2

Try this:

SQL

select a.name, b.course, c.year_completed
from a join c on a.id=c.a_id join b on b.id=c.b_id
where c.b_id = (select max(b_id) from c where c.a_id=a.id)
order by c.year_completed desc

Posted 18-Aug-15 3:39am

Peter Leow