Answer / anuradha

The unique column constraints permits multiple entries of
null in the column. these null values are clubbed at top of
column in order they were entered into table. this is
essential difference .

Table have more than 1 unique key which is not possible in
primary key

Answer / chauhan rakesh botad

Primary key doesnot allow null value but unique key allows
null value. We can declare only one primary key in a table
but a table can have multiple unique key(column assign).

Answer / pawan mishra

One table may have more than one Unique Key Constraint
columns, but should have only one Primary Key Constraint
column.

Answer / ibrahim

PRIMARY KEY is identity of each row. UNIQUE KEY also
identity of each row.
PRIMARY KEY not accepts null values but unique can accept null.

but the core different between primary key and unique is we use primary key to link tow tables with each other but we can not use unique key to do this.

Answer / pandiyan

Primary key doesnot allow null value but unique key allows
null value.

Answer / chetan sharma

Primary key creates Clustered Index.
Unique key creates non-clustered Index.

the no of primary key in a table is one but the no of
unique is more then one

there is only one primary key for one table;
it can not acept null values;
any no uniquefor a table;
it can accept null values;
which the rows are unique value;

Answer / lucky

Primary key not accepts to null values in database, but
uniqe key accepts to the null values in database.

Each table having only one PRIMARY KEY.And my contain many
UNIQUE KEYS.
PRIMARY KEY is identity of each row. UNIQUE KEY also
identity of each row.
BOTH keys will not contain repeated value.
BUT UNIQUE KEY will contain NULL value but PRIMAY key will
not contain NULL value.

Answer / pramod paunikar

Both primary key and unique enforce uniqueness of the
column on which they are defined. But by default primary
key creates a clustered index on the column, where are
unique creates a non-clustered index by default. Another
major difference is that, primary key does not allow NULLs,
but unique key allows only one NULL only.

Answer / manoj routh

Both primary key and unique enforce uniqueness of the column
on which they are defined. But by default primary key
creates a clustered index on the column, where are unique
creates a nonclustered index by default. Another major
difference is that, primary key doesn't allow NULLs, but
unique key allows one NULL only.

Answer / sikander

Primary key does not allow null value but unique key allows
null value. suppose tableA two column : columnB & columnC .
where coulmnB is primary key & columnC is unique key.
If we insert null value in columnB.It will not accept
columnB but columnC

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