SQL query issue with achieving an encompasses all effect - sql

Question

Below is the query I have been working on for this question.
Find the names of the companies which have employees residing in every city where employees of Mutual of Omaha live.
This means that if Mutual has employees in the cities Omaha, Lincoln, and Denver that the only company names it should return is a company that has employees in all 3 of those cities. This should also return Mutual.
The below query returns the company which has an employee in any of those three cities. The lastname is there for me to manually check which employees it is counting.
SELECT COMPANY_NAME, e1.lastname
FROM EMPLOYEE E1,WORKS W1
WHERE E1.CITY IN (SELECT CITY
FROM EMPLOYEE E2,WORKS W2
WHERE E2.firstname = W2.firstname
AND E2.lastname = W2.lastname
AND W2.COMPANY_NAME= 'Mutual of Omaha')
AND E1.firstname = W1.firstname
AND E1.lastname = W1.lastname;
I realized I didn't put the tables down so here they are
employee (Lastname, FirstName, MidInitial, gender, street, city)
works (Lastname, FirstName, MidInitial, company_name, salary)
manages(Lastname, FirstName, MidInitial, ManagerLastname, MFirstName, MMidInitial, start-date)

Answer 1

It's not the most elegant piece of code, but try using this one:
WITH tab AS (
SELECT DISTINCT W1.COMPANY_NAME,
E1.CITY
FROM EMPLOYEE E1
JOIN WORKS W1 ON (E1.firstname = W1.firstname AND E1.lastname = W1.lastname)
WHERE E1.CITY IN (SELECT DISTINCT E2.CITY
FROM EMPLOYEE E2,WORKS W2
WHERE E2.firstname = W2.firstname
AND E2.lastname = W2.lastname
AND W2.COMPANY_NAME= 'Mutual of Omaha')
)
SELECT tab.COMPANY_NAME
FROM tab
GROUP BY tab.COMPANY_NAME
HAVING COUNT(tab.CITY) = (SELECT COUNT(sub.CITY) FROM tab sub WHERE COMPANY_NAME = 'Mutual of Omaha')

Answer 2

This option uses the bitwise operator so is also limited by the number of cities it can use at once (~31 due to Int size limit)
------------Assign each distinct city a value that is x2 the previous (like binary counting)
create table #cityvalues (CityName varchar(100), ValueField int)
select distinct E1.CITY
into #while
FROM EMPLOYEE E1
while (select count(*) from #while) > 0
begin
insert into #cityvalues
select top 1 CITY, coalesce((select max(ValueField) from #cityvalues)*2, 1) from #while
delete from #while w where w.CITY in (select CityName from #CityValues)
end
--------------------------------------------------------------------------------
--------------Create a list of Company/City--------------------------------
create table #companycities (Compname varchar(100),CityName varchar(100))
insert into #companycities
select distinct
W1.COMPANY_NAME
,E1.CITY
FROM EMPLOYEE E1
JOIN WORKS W1 on E1.firstname = W1.firstname AND E1.lastname = W1.lastname
----------------------------------------------------------------------------
----This SUM function then creates a "list" of all cities for the company in a single field
select cc.Compname, sum(cv.ValueField) as AllCities
into #CompanyAllCities
from #companycities cc
join #cityvalues cv on cc.CityName = cv.CityName
group by Compname
-----------------------------------------------------------------
----------This query checks if the company's "list" contains the "list" for the joined company, excluding itself
select distinct cac1.Compname
from #CompanyAllCities cac1
join #CompanyAllCities cac2 on cac2.Compname = 'Mutual'
where cac2.AllCities & cac1.AllCities = cac2.AllCities
and cac1.Compname <> 'Mutual'
-------------------------------------------------------------
----------Tidy up after yourself----------
drop table #cityvalues,#CompanyAllCities,#companycities
-----------------------------------------

Answer 3

I would start with a CTE that has each company with the cities they operate in.
Then there are several options, but a self-join with aggregation does the count that you want:
with cw as (
select distinct e.city, w.company_name
from employee e join
works w
on e.firstname = w.firstname and
e.lastname = w.lastname and
e.midinitial = w.midinitial
)
select cw.company_name
from cw join
cw cwo
on cw.city = cwo.city and
cwo.company_name = 'Mutual of Omaha'
group by cw.company_name
having count(*) = (select count(*) from cw where
cw.company_name = 'Mutual of Omaha');

Answer 4

You can list and weight the cities where companies have employees, so you will get a single number representing each company based on where they have their employees, a sort of group number.
Then you can check which cities have the same group number.
;with
cities as(select ROW_NUMBER() over (order by city) city_id, city from (select distinct city from employees) c),
chk as (
select distinct company_name, city_id
from works w
join employees e on w.firstname = e.firstname and w.lastname = e.lastname
join cities c on c.city = e.city
),
cnt as (
select company_name, SUM(power(cast(2 as bigint), city_id-1)) n
from chk
group by company_name
)
select company_name
from cnt
where n = (select n from cnt where company_name = 'Mutual of Omaha')