Answer / romee

Unique Key is a candidate key to uniquely identify each
row in a table.

Answer / guest

It is a constraint used to avoid duplication of values
within the row of a specified column or set of columns in a
table. It can also allow null values

Answer / jai

UNIQUE key is a constraint which can be applied on a data
base table column for uniquely identifying the values in
that column but the column can contain NULL values.

without duplicates but with NULL values

Answer / koteswara rao.k

suppose you have landline and through the landline you have
taken net connection .
so at the end of the month you will get two bills on the
landline which is subject to one means

primary key is landline which is parent one ( customer
code available)
broadband and landline ( two bills generation ) are the
unique keys called child keys .(contract ids available)
so in this scenario contract ids can be null but cannot be
duplicate .
One more You cannot remove the primary key until and unless
remove the branched ones.

I have good knowledge on GSM /broadband/pstn technologies .
Any wrong ping with me pls koteswara.9.rao@gmail.com

Answer / abhishek.421

a sort of primary key..just it allows NULL values

Answer / vital reddy

suppose you have landline and through the landline you have
taken net connection .
so at the end of the month you will get two bills on the
landline which is subject to one means

primary key is landline which is parent one ( customer
code available)
broadband and landline ( two bills generation ) are the
unique keys called child keys .(contract ids available)
so in this scenario contract ids can be null but cannot be
duplicate .
One more You cannot remove the primary key until and unless
remove the branched ones.

I have good knowledge on GSM /broadband/pstn technologies .

Answer / guest

It is y=the unique value with nulls.

Answer / neo devan

Any key may/maynot satisfy 2 conditions :
* Not Null
* Unique
Unique key is tne one which satifies the second condition
but it can have null values.

Answer / ambresh pratap srivastava

primary key is combination of column which uniquely specify a row.A table have at most one primary key. primary key creates Clustered Index.A primary key column allows no row having null value

Unique key can uniquely identify each row in a table and is closely related to super key concept.A unique key comprises a single column or a group of column.A unique key column allows only one row having null value.Unique key creates unclustered Index.

Answer / gyana ranjan behera

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.

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