how to use two primary keys in table

Take a look at the below links that show how to create composite Primary keys
Creating composite primary key in SQL Server[^]
How to create composite primary key in SQL Server 2008[^]
SQL Server Add Primary Key[^]
Composite Primary Keys[^]

You can have only one primary key in a table. Although, this does not mean that it should be only one column. You can use two columns as primary key. Here's an example:

CREATE TABLE SampleTable (
  Key1 integer,
  Key2 integer,
  SomeOtherColumn nvarchar
  primary key (key1, key2)
);

You might also want to consider Unique constraint.

Hi,

If you believe that you need 2 primary keys it looks like your data is not normalised.

It is highly likely that you will need to split your table in to two and maybe also require a link table to map the primary keys of table1 to table2.

If two columns together give you your unique reference then a composite key should be used. To achieve this, in design view of the table select both fields simultaneously and click on the key icon.

If still unsure please post a sample of your table with an explanation.

Hope this helps.

From what you have said in comments, I think what you actually want to do is to make the second column (EnrollmentNo) unique? You can do this without specifying it as a primary key.

see here[^]

Each table can have only ONE primary key.
Y dont you go for foreign key relation for the same table