Selecting objects that are associated with similar datasets - sql

Question

I'm trying to select all company rows from a [Company] table that share with at least one other company, the same number of employees (from an [Employee] table that has a CompanyId column), where each group of respective employees share the same set of LocationIds (a column in the [Employee] table) and in the same proportion.
So, for instance, two companies with three employees each that have the locationIds 1,2, and 2, would be selected by this query.
[Employee]
EmployeeId | CompanyId | LocationId |
========================================
1 | 1 | 1
2 | 1 | 2
3 | 1 | 2
4 | 2 | 1
5 | 2 | 2
6 | 2 | 2
7 | 3 | 3
[Company]
CompanyId |
============
1 |
2 |
3 |
Returns the CompanyIds:
======================
1
2
CompanyIds 1 and 2 are selected because they share in common with at least one other company: 1. the number of employees (3 employees); and 2. the number/proportion of LocationIds associated with those employees (1 employee has LocationId 1 and 2 employees have LocationId 2).
So far I think I want to use a HAVING COUNT(?) > 1 statement, but I'm having trouble working out the details. Does anyone have any suggestions?

Answer 1

This is ugly, but the only way I can think of to do it:
;with CTE as (
select c.Id,
(
select e.Location, count(e.Id) [EmployeeCount]
from Employee e
where e.IdCompany=c.Id
group by e.Location
order by e.Location
for xml auto
) LocationEmployeeData
from Company c
)
select c.Id
from Company c
join (
select x.LocationEmployeeData, count(x.Id) [CompanyCount]
from CTE x
group by x.LocationEmployeeData
having count(x.Id) >= 2
) y on y.LocationEmployeeData = (select LocationEmployeeData from CTE where Id = c.Id)
See fiddle: http://www.sqlfiddle.com/#!6/6bc16/5
It works by encoding the Employee count per Location data (multiple rows) into an xml string for each Company.
The CTE code on its own:
select c.Id,
(
select e.Location, count(e.Id) [EmployeeCount]
from Employee e
where e.IdCompany=c.Id
group by e.Location
order by e.Location
for xml auto
) LocationEmployeeData
from Company c
Produces data like:
Id LocationEmployeeData
1 <e Location="1" EmployeeCount="2"/><e Location="2" EmployeeCount="1"/>
2 <e Location="1" EmployeeCount="2"/><e Location="2" EmployeeCount="1"/>
3 <e Location="3" EmployeeCount="1"/>
Then it compares companies based on this string (rather than trying to ascertain whether multiple rows match, etc).

Answer 2

An alternative solution could look like this. However it also requires performance testing in advance (I don't feel quite confident with <> type join).
with List as
(
select
IdCompany,
Location,
row_number() over (partition by IdCompany order by Location) as RowId,
count(1) over (partition by IdCompany) as LocCount
from
Employee
)
select
A.IdCompany
from List as A
inner join List as B on A.IdCompany <> B.IdCompany
and A.RowID = B.RowID
and A.LocCount = B.LocCount
group by
A.IdCompany, A.LocCount
having
sum(case when A.Location = B.Location then 1 else 0 end) = A.LocCount
Related fiddle: http://sqlfiddle.com/#!6/d9f2e/1