These queries are same they are retriving the fname ,lname of employee who have dependent with same first name ,lname as that of employee - my doubt is that in second query why we are not taking the condition e.ssn=d.essn
1): SELECT E.Fname, E.Lname
FROM EMPLOYEE AS E
WHERE EXISTS ( SELECT *
FROM DEPENDENT AS D
WHERE E.Ssn=D.Essn AND E.Sex=D.Sex
AND E.Fname=D.Dependent_name);
2)SELECT E.Fname, E.Lname
FROM EMPLOYEE AS E
WHERE E.Ssn IN ( SELECT Essn
FROM DEPENDENT AS D
WHERE E.Fname=D.Dependent_name
AND E.Sex=D.Sex );
