How to do sum of column when there is 1million records

Yes, doing a sum when there are a million records in the table takes the database longer than doing a sum with a few thousand records.  If you have performance problems, you might have to add an index.  For example, suppose you had this SQL:

select SUM(sale_price)
from sales
where store_id = 57

If you have millions of records, you might need to put an index on the store_id column to improve performance. 

Hi,
I mean to ask it will take more time to fetch the record from millions of record?

If you just want the sum, nothing else, you should use a simple SQL query to let the database do it.  You should NOT try fetching 1 million records to the web server and then try to sum them there.  That would be slow. 

select SUM(sale_price) from sales

The database can do this kind of thing very efficiently.

That data should be in a partitioned table but that option is available only in the Enterprise, Development or Eval version of SQL Server.

Otherwise you can use a partitioned view which logically splits a large table into smaller tables.