Database Systems 6th Edition by Ramez Elmasri, Shamkant B. Navathe

تمرين 9

-Consider the EMPLOYEE table's constraint EMPSUPERFK as specified in Figure 4.2 is changed to read as follows: CONSTRAINT EMPSUPERFK FOREIGN KEY (SUPERSSN) REFERNCES EMPLOYEE(SSN) ON DELETE CASCADE ON UPDATE CASCADE, Answer the following questions:
a. What happens when the following command is run on the database state shown in Figure 3.6?
DELETE EMPLOYEE WHERE LNAME = 'Borg'
b. Is it better to CASCADE or SET NULL in case of EMPSUPERFK constraint ON DELETE?