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Using GUID or UniqueIdentifiers in SQL Server

In order to differentiate between two rows, we normally use primary keys or identity values which may be same across two tables. In order to overcome this problem we can use a special type named "GUID". Its a hexadecimal number (Base 16) and the advantage is 
that they are unique across all databases and tables. 

 In SQL Server the same concept is implemented through UNIQUEIDENTIFIER data type. In order to generate a new value, we use the NEWID() function.

 For e.g. 

a. Creating a table that uses the UNIQUEIDENTIFIER datatype

 Create table Test
(
Empno uniqueidentifier,
Ename varchar(20)
)

b. Inserting rows in the tables with the use of NEWID() function
insert into Test values (newId(),'ABC')
insert into Test values (newid(),'XYZ')

insert into test values (newid(),'MNO')

 c. Selecting the rows from the table.

 Select * from test 

 Empno                                                                     Ename
6B2CF0E5-DC2E-4EB5-A090-71AD6C0EE260 ABC
917470F4-C165-4F21-8894-942C91E56BA9         XYZ
C7F3E70E-9972-45C6-A847-B4489F4B05FC MNO

 So we can see that the first column i.e. Empno is containing values that are unique and they are of type UniqueIdentifier. Its another way of having primary key in the table.

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