what is the different between unique+not null & primary key,

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what is the different between unique+not null & primary key,..

Answer / sreekumar

In a relation, we can create only one primary key where as we can create multiple unique+not null constrains.

Primary key uses clustered index where are unique +Not null uses non clustered index.

Sreekumar

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what is the different between unique+not null & primary key,..

Answer / suresh babu

Unique:

Unique is a constraint,which doesn't allow the duplicate
values and allow only one null value.We can create more
number of unique constraint in single table.

Not Null:

Not Null constraint,which doesn't allow the Null values and
allow the duplicate values.

Primary Key:

We can create one primary key for a table,Which doesn't
allow the duplicate and null values,and used for make a
foreign key relation.we can't do this process using above
two constraints.

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what is the different between unique+not null & primary key,..

Answer / mohan babu

A unique key is nothing but it does not allow any
duplicateds but allows nullvalues

A primary key is nothing but it does not allow duplicates
as well as Null values i.e Not Nulls

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what is the different between unique+not null & primary key,..

Answer / giri

unique:it does not allow duplicate values but it allow null values.
not null:It does not allow null values but allow duplicate values.
primary:It does not allow both duplicate and null values.

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