Answer / tulsi

Primary key will avoid duplicate and null values in a table
which the combination of unique+not null will do.But the
advantage is,if a table has primary key we can create
relation to child tables.

Answer / shilpa.oracle

Primary key accepts only unique values and does not allow
null values.

Unique key accepts unique values and allows null values.

not null constraint allows duplicate values and doesnt allow
null values.

When a primary key constraint or unique key constraint is
created by default index is created on the columns with
these constraints.

Answer / smita

A Foriegn key can refer to the primary key.
A Foriegn key can refer to the unique key also .

Answer / soubhagya

When we create a primary key automatically a cluster index
is created on those columns involved in primary key.But
this index not created in unique+not null key, it only
restrict the duplicate values.

Answer / kamal

we are able to create a primary key for combination of more
than 1 column. which is not possible in Unique,we should
create unique key for each and every column in the table
individually.

ex . we can create a primary key for (Name,DOB,address)- ie
combination of these three columns be unique.

Answer / charumathi

Unique-Duplicates not allowed
Nulls allowed
Not null-NUlls not allowed
Primary key-No Duplicates
No Nulls
A Foriegn key can refer to the primary key.

Answer / nitesh

PRIMARY KEY CREATED WITH INDEXES WHICH IS NOT HAPPEN WITH
UNIQUE AND NOT NULL

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