Question

So there are three tables that would be applicable in this statement. The division table, which houses the division name and division id, the workon table which houses the projects and employee ids that correlate to the project, and the employee table that houses the employee id, department id, and name. I’m trying to find the department that has the most employees who work on projects.

This is my code:

select distinct 
    (dname) as "Division Name"
from 
    employee e, division d
where 
    d.did = e.did and 
    d.did in (
        select did from employee where empid in (
            select empid from workon having count(pid) >= all(pid)
        )
    )

I’m supposed to get the answer “human resources” but I cannot seem to get that answer no matter what code I use.

Workon table

PID EMPID   HOURS
3   1   30
2   3   40
5   4   30
6   6   60
4   3   70
2   4   45
5   3   90
3   3   100
6   8   30
4   4   30
5   8   30
6   7   30
6   9   40
5   9   50
4   6   45
2   7   30
2   8   30
2   9   30
1   9   30
1   8   30
1   7   30
1   5   30
1   6   30
2   6   30

Employee Table

EMPID   NAME    SALARY  DID
1   kevin   32000   2
2   joan    42000   1
3   brian   37000   3
4   larry   82000   5
5   harry   92000   4
6   peter   45000   2
7   peter   68000   3
8   smith   39000   4
9   chen    71000   1
10  kim 46000   5
11  smith   46000   1

Division
DID DNAME   MANAGERID
1   engineering 2
2   marketing   1
3   human resource  3
4   Research and development    5
5   accounting  4

Answer 1

Check this reference out please.

SQLFIDDLE

select d.id, d.name, p.maxcounts
from dept d, 
(select we.dep, max(we.counts) as maxcounts 
 from (select w.eid, count(w.pid) as counts, 
 e.dep as dep from employee e, workon w
where e.id = w.eid
group by e.dep) as we) as p
where d.id = p.dep
;

RESULTS:

ID      NAME                MAXCOUNTS
111     human resoruces     5

FOLLOWING is the edit based on your own data:

Reference : SQLFIDDLE_Based_ON_OP_Data

There are three ways you can achieve this. Either use the nested selects, save Max(count) into a variable or order data by desc and limit it to 1.

Method 1:

— using nested select

—sub query 1 explaining to OP how final answer is derived

select e.dep, count(w.eid) as num_emp
from employee e, workon w
where e.id = w.eid
group by e.dep
order by e.dep
;
-- **results of sub query 1:**

DEP     NUM_EMP
1           4
2           5
3           7
4           5
5           3

— Final nested select query

select ee.dep, dd.name, count(ww.eid)
from employee ee, dept dd, workon ww
where ee.id = ww.eid
and ee.dep = dd.id
group by ee.dep, dd.name
having count(ww.eid) = 
(select distinct max(t.num_emp)
from (select e.dep, count(w.eid) as num_emp
from employee e, workon w
where e.id = w.eid
group by e.dep
order by e.dep)as t)
;

— results using nested selects

DEP     NAME            COUNT(WW.EID)
3       human resource  7

— query using a variable

select max(x.num_emp) into @myvar from 
(select e.dep, count(w.eid) as num_emp
from employee e, workon w
where e.id = w.eid
group by e.dep) as x
;


select x.dep, x.name, x.num_emp as num_emp from 
(select e.dep, d.name, count(w.pid) as num_emp
from employee e, workon w, dept d
where e.id = w.eid
and e.dep = d.id
group by e.dep) as x
where x.num_emp = @myvar
;

— results using variable

DEP     NAME              NUM_EMP
3       human resource    7

— query using limit 1 with ordered desc table

select e.dep, d.name, count(w.eid) as num_emp
from employee e, workon w, dept d
where e.id = w.eid
and e.dep = d.id
group by e.dep
order by num_emp desc 
limit 1

— results using order by desc and limit 1:

DEP     NAME              NUM_EMP
3       human resource    7

Now when using Method 3, it may or may not matter to you that sometimes there will be two departments with same highest number of employees working in projects. So in that case you may use either nested or variable methods.

*PS I do not have the privilledge to be full time on StackOverFlow, hence sorry for getting back to you late 🙂 *