Avinash Byalihal

• Aug 8th, 2006

 

Declare that column as UNIQUE and add constraint as NOT NULL.Hope this helps u.

Rama Krishna

• Aug 9th, 2006

 

Hi Gupta!!

The Major Advantage of PKey is Its being INDEXED and the perofrmance going to increase..

Thanks&Regds

Ramki,

TCS,Dp,Hyd

Rajesh

• Aug 11th, 2006

 

As per my knowledge is concerned..

if already you have created a primary key on one table and in that same table another column is there, which is also mandatory for you- in that context you have to use Unique key and add not null constraint.

Rajesh

Amlan sarkar

• Aug 15th, 2006

 

Hi ,

The concept of adding an unique key and not null constraint to a column as well as adding as unique index to it , you will assume to get the  benefits  of adding an primary key to that column.

But use it for the purpose of referential integrity will not allow to do so.

That's what PK is so useful. You will use it for normalization purpose.

Hope things are clear now.

Regards

Amlan

vishalreddy

• Aug 29th, 2006

 

this is not possible.

manohar

• Sep 14th, 2006

 

hi,primary key is nothing but unique+not null+indexes......

chary

• Jul 9th, 2007

 

Apart from null and not not null context, when both primary key and unique key uniquely identifies an row.... in a table, what is the major difference between them

waiting for reply......


Thanks

as_anand_kumar

 Profile Answers by as_anand_kumar 

• Aug 14th, 2011

 

SQL>
SQL> create table temp (empno number not null);

Table created.

SQL> alter table temp add constraint temp_empno unique(empno);

Table altered.

SQL>

Parmita Mallick

• Sep 7th, 2011

 

unique key are also indexed. PRIMARY KEY is clustered index whereas UNIQUE KEY is non clustered.

z_ashwini

 Profile Answers by z_ashwini 

• Jan 13th, 2012

 

Eg:

Consider table emp with EMP_ID,EM|NAME,ADD columns

You can define the column e_name as Unique constraint.

DECLARE
e_name number(10) NOT NULL;
BEGIN
...
..
END:

Primary key cannot have NULL values and is unique.
One table can have single primary key.
Suppose you have already defined EMP_ID as primary_key in the previous example and if you want NOT NULL and Unique values then you can use the above alternative.

Best Regards,
Ashwini Likhite

Vinod Tuteja

• Jun 14th, 2013

 

Main Difference : Referential
Index is created in both Cases (Unique and Primary key Constraint )

But can't references Columns with combination of UNIQUE and NOT NULL. Like in Primary key ,we Can references primary key to make foreign key constraint .