Question

The null values are not allowed to appear in a
field
A. Foreign key B. Candidate key
C. Primary key D. Super key
​

Answer 1

Primary Key can not be null

Primary key

Primary key is a column or group of column which provide unique identity to each and every row of a table. Primary key can never be null value.

Extra information

There can not be more than one primary key

but you can give this type of property to another column by using or applying unique key and not null key then it will act as primary key.

primary key = uniquee key + not null key