Some Explanation at Unique key

[firoz.raj]

Can anybody tell me the difference between a Primary key and
a Unique Key ?Kindly let me know the idea.Any help would be
highly appreciated.

[debasisdas]

Unique key enforces only uniqueness (no duplicate) where as a Primary key enforces both uniqueness and not null (data must be entered into the field). Once a PK is created on a column oracle creates an index on the column.

[firoz.raj]

generally if i want primary key in ms access table.i just w.c on the
filed .and access create primary key.But how should i make Unique
Key in Ms Access table .Kindly let me know the idea.any help would
be highly appreciated.

[debasisdas]

You need to change the field properties.

[gana poduval]

Bothe Primary key and unique constraints are using to uniquly identify the each record in the database.
The main Differnce are,.

1)There is only one primary key in one table but we can have multiple unique key in one table
2)We can have null value in Unique key column but we cannot have null value in primary key column.