Answer / kalpana

Primary key can never be NULL.it is used to uniquely
identify the row in a table.The database engine requeir a
value to relocate the record.so Primary key can never be
NUL.unique key may be NULL.

Answer / sunil kumar

Hello Nivedita,
I am not satisfied with ur answer the difference between
primary key and foreign key.I think the answer is reverse.

Answer / bharanikumar

primary key does not allow null value,
but unique allow only one null value...


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Answer / amit kumar tiwari

primary key uniquely define each table and never allow NULL
value. But unique key may be NULL value.

Answer / g priya

If a field is null the database engine makes the field to be 0
if not null is specified ,field must be given a value
Primary key is unique,not null,index where as Unique key has
1 null value

Answer / nivedita

IF NULL is specified,the feild is allow to be left empty
without any value.
IF NOT NULL is specified,the field must be given a value. In
the absence of either a NULL or NOT NULL, NULL is assumed.

-------
Unique key can't be NULL.Primary key can be NULL.
Unique key always contain unique value,duplicate are not
allowed(genrally the system genrated key).Primary key maybe
repeated.

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