Which of the following is the primary key of the table below (you can assume the data are representative)?
|
STAFF_NUM
|
STAFF_NAME
|
BRANCH_NUM
|
BRANCH_ADDRESS
|
POSITION
|
|
S100
|
Smith, J
|
B100
|
Pseudopolis
|
Manager
|
|
S100
|
Smith, J
|
B200
|
Ankh
|
Sweeper
|
|
S295
|
Vetinari, H
|
B100
|
Pseudopolis
|
Patrician
|
|
S331
|
Colon, S
|
B100
|
Pseudopolis
|
Clerk
|
Select one:
a. STAFF_NUM
b. There is no primary key because STAFF_NUM repeats meaning this is not a valid relation
c. BRANCH_NUM
d. STAFF_NUM, BRANCH_NUM