V popisu sloupce vaší výsledkové tabulky nevidím minit, address and number of occurrences
. Proto bych váš výběr zjednodušil na:
SELECT e1.ninumber,
e1.fname,
e1.lname,
e1.superNiNumber,
FROM employee AS e1,
employee AS e2
WHERE e1.dno = 8
AND e1.superNiNumber = e2.ninumber
AND e2.dno = 8
and (select count(*) from employee e3
where e3.superNiNumber = e1.superNiNumber) > 1;