Question

I have 2 tables structured like this:

People
----------
>ID, Name, Surname

Projects
----------
>ID, Assistant#1,  Assistant#2,  Assistant#3,  Assistant#4, 
> Assistant#5,  Assistant#6,  Assistant#7,  Assistant#8,  Assistant#9, 
> Assistant#10, lot of other columns..... (every assistant column
> contains an integer, the people ID)

Now, I want to query my DB and get a single row from Project table (let’s suppose row with ID=3) containing all columns of project table and in particular have each assistant replaced with it’s correct name and surname.
I’ve managed to do this (with a lot of joins), but with my little sql experience my code looks very bulky and i’m sure that there’s a better way to do this.

Thanks in advance.

Answer 1

Because you set a number of (possible) assistants at 10, that dictates that you are going to have to write code to accomodate those 10 assistants. This can be done a few ways: (have not tested)

select * from projects proj
left join people p1 on proj.assistant1 = p1.peopleid
left join people p2 on proj.assistant2 = p2.peopleid
left join people p3 on proj.assistant3 = p3.peopleid
left join people p4 on proj.assistant4 = p4.peopleid
left join people p5 on proj.assistant5 = p5.peopleid
left join people p6 on proj.assistant6 = p6.peopleid
left join people p7 on proj.assistant7 = p7.peopleid
left join people p8 on proj.assistant8 = p8.peopleid
left join people p9 on proj.assistant9 = p9.peopleid
left join people p10 on proj.assistant10 = p10.peopleid

otherwise you could do some trickery with

select proj.projectID, 
(select * from people where peopleID = proj.assistant1),
(select * from people where peopleID = proj.assistant2),
(select * from people where peopleID = proj.assistant3),
(select * from people where peopleID = proj.assistant4),
(select * from people where peopleID = proj.assistant5),
(select * from people where peopleID = proj.assistant6),
(select * from people where peopleID = proj.assistant7),
(select * from people where peopleID = proj.assistant8),
(select * from people where peopleID = proj.assistant9),
(select * from people where peopleID = proj.assistant10)
from projects proj

If possible, it might be best to re-structure your datatables, and have a single assistant mapped to a single projectID:

PeopleID, Name, Surname

ProjectID, PeopleID

Therefore, you could do just one inner join and you will return a row for each assistant:

select * from projects proj 
inner join people p 
on p.peopleID = proj.peopleid
where proj.projectID = PROJECTID