Consider the following SQL query:
PROJ(Pnum, Dnum)
DEPT(Dnumber, Mgr_Ssn)
EMP(fname, lname, Ssn)
Works_ON(Pno, ESSn)
(SELECT DISTINCT Pnum
FROM PROJ, DEPT, EMP WHERE Dnum = Dnumber
AND Mgr_ssn = Ssn AND Lname=’XXXX’)
UNION
(SELECT DISTINCT Pnum FROM PROJ, WORKS_ON, EMP WHERE Pnum=Pno AND ESSn=Ssn
AND Lname=’XXXX’)
1
all project numbers for projects that involve an employee with last name ‘XXXX’, either as worker or as manager
2
all project numbers for projects that involve an employee with last name ‘XXXX’ as manager
3
records of all employees with last name as ‘XXXX’ working in a project as manager
4
All project numbers for projects in department Dnumber and where ‘XXXX’ is involved either as worker or as manager