Go4Expert

Go4Expert (http://www.go4expert.com/)
-   SQL Server (http://www.go4expert.com/forums/sql-server-forum/)
-   -   Primary key VS Unique key in SQL Server (http://www.go4expert.com/forums/primary-key-vs-unique-key-sql-server-t9260/)

venkatesanj@hcl.in 12Mar2008 08:36

Primary key VS Unique key in SQL Server
 
Unique Key constraints:

Unique key constraint will provide you a constraint like the column values should retain uniqueness.
It will allow null value in the column.
It will create non-clustered index by default
Any number of unique constraints can be added to a table.


Code:

CREATE TABLE EMPLOYEETABLE
        (EMPID INT ,
        IDVAL INT NOT NULL, 
        FIRSTNAME VARCHAR(30) ,
        LASTNAME VARCHAR(30) ,
        CITY VARCHAR(30),
        JOININGDATE DATETIME)

I have created a table EmployeeTable and i am trying add a unique constriant on the column IDVAL.

Code:

ALTER TABLE EMPLOYEETABLE
 ADD CONSTRAINT UNIQUE_CONSTRAINT
 UNIQUE (IDVAL)


Primary Key:
Primary key will create column data uniqueness in the table.
Primary key will create clustered index by default
Only one Primay key can be created for a table
Multiple columns can be consolidated to form a single primary key
It wont allow null values.


Code:

ALTER TABLE EMPLOYEETABLE
 ADD CONSTRAINT KEY_CONSTRAINT
 PRIMARY KEY (IDVAL)

Please provide me your valuable feedback regarding this article.

Regards,
Venkatesan Prabu . J


All times are GMT +5.5. The time now is 12:23.