Question

This was a question which I was asked in an interview recently:

You have various types of users in an organization : Junior (is bossed by) Supervisor (is bossed by) Manager (is bossed by) CEO.

We agreed upon this single simplified table schema. Users : {userId, userName, UserType(J, S, M, C), bossUserId}

Q : Write a single query to determine the complete organizational hierarchy of a Junior employee with userId = 11.

Sample Data :

The answer would be => PQR2 --> GHI2 --> DEF1 --> ABC1

This was my solution :

select e1.userName, e2.userName, e3.userName, e4.userName from 
abc e1 inner join users e2 on e1.bossUserId = e2.userId
inner join users e3 on e2.bossUserId = e3.userId
inner join users e4 on e3.bossUserId = e4.userId
where e1.userId = 11;

I do realize that self joining 4 times is horrible, but I was not able to think of anything else. The interviewer told me that there is a better way and that the data will show up columnwise. (using a maximum of 2 self joins, if at all)

Another possibility was to write a stored procedure, but again it is not a single query.

Can anyone help me with this?

Answer 1

Following your comments, in MS SQL (and others, similarly) you can do this

;with cte as (
    select *, 0 as level from yourtable
    union all 
    select cte.id, t2.name, t2.ut, t2.bossid, level+1
    from cte
        inner join yourtable t2 on cte.bossid = t2.id
)
    select name, ut from cte
    where id=11
    order by level

which gives you

pqr2    j
ghi2    s
def1    m
abc1    c

But MySQL doesn’t support this construct.