How to find out employees having same department but different shifts - sql

Question

I have a table employee which has different attributes like emp_code, naeme,...., deptt.
There is another table called nightShift which has fields- emp_code, shift_time.
Any employee which is not in nightShift table is automatically assumed to be in day shift.
Now I have to find out those deptt which has some employees working in night shift and some in normal shift
What can be a query for this.
Example
**Employees**
----------------------------------------
emp_code| Name | deptt
----------------------------------------
e1 John Ops
e2 Martin Ops
e3 Gary Infra
e4 John Facilities
e5 Michael Ops
e6 Alan Ops
e7 Tony Facilites
e8 Alex Infra
e9 Peter Infra
e10 Ron Ops
**nightShift**
----------------------------------------
emp_code | shift_time
----------------------------------------
e1 shiftA
e2 shiftA
e5 shiftB
e4 shiftB
e7 shiftC
Now in the output, I want only Deptt Ops, as some of its employees are in night shift(e1,e2,e5) and some in normal shift(e6,e10)
The output should NOT contain Infra as all employees(e3,e8,e9) are in normal shift and none in night shift.
The output should NOT contain Facilities as all employees(e4,e7) are in night shift and none in normal shift.
Can somebody help me with this?

Answer 1

Here is a group by version - join both tables in a left join and count nightShifts per department. If count is greater than zero but not equal to count of all workers in department, we have a match.
select employees.deptt
from employees
left join nightShift
on employees.emp_code = nightShift.emp_code
group by employees.deptt
having count (nightShift.emp_code) > 0
and count (employees.emp_code) <> count (nightShift.emp_code)
Test it on Sql Fiddle.

Answer 2

You could try something along these lines
select
distinct e.deptt
from
Employees e
inner join
NightShift n
on
n.emp_code = e.emp_code
Where
e.deptt not in ('Facilities', 'Facilites')
The inner join will eliminate everyone not working night shifts, then in the where we find any results not working in deptt Facilities

Answer 3

I think you need to count the number of night shift workers for each department, and the number of day shift workers for each department, and you're concerned with those departments where both counts are bigger than zero.
Stage 1: Night shift workers per department:
SELECT e.deptt, COUNT(*) AS headcount
FROM Employees AS e
JOIN NightShift AS n
ON n.emp_code = e.emp_code
GROUP BY e.deptt
Stage 2: Day shift workers per department
There are various possible strategies for this. One is to count the total workers for each department and subtract the number of nightshift workers:
SELECT d.deptt, (d.headcount - n.headcount) AS headcount
FROM (SELECT e2.deptt, COUNT(*) AS headcount
FROM Employees AS e2
GROUP BY e2.deptt
) AS d
JOIN (SELECT e.deptt, COUNT(*) AS headcount
FROM Employees AS e
JOIN NightShift AS n
ON n.emp_code = e.emp_code
GROUP BY e.deptt
) AS n
ON d.deptt = e.deptt
Stage 3: Pick those departments where the headcounts on the dayshift and night shift are both non-zero:
SELECT d.deptt, (d.headcount - n.headcount) AS dayshift, n.headcount AS nightshift
FROM (SELECT e2.deptt, COUNT(*) AS headcount
FROM Employees AS e2
GROUP BY e2.deptt
) AS d
JOIN (SELECT e.deptt, COUNT(*) AS headcount
FROM Employees AS e
JOIN NightShift AS n
ON n.emp_code = e.emp_code
GROUP BY e.deptt
) AS n
ON d.deptt = e.deptt
WHERE d.headcount > 0
AND n.headcount > 0
There might be a more succinct formulation, but I'm fairly sure this would give the correct answer.
Subject to the note that this has not been anywhere near an actual SQL DBMS so there could be some syntax errors in it.
I'm also assuming you're using a supported version of Informix (and not Informix OnLine or Informix SE). Some older versions of Informix would not support all this syntax but I believe all the 11.x versions (which are all currently supported) should all handle these queries.
You can probably simplify this along the lines of Nikola Markovinović's answer.