Comma seperated decimal column

Using the below way we can conver the decimal to be shown as comma seperated string

DECLARE @Test DECIMAL(20,4)

SET @Test = 123123123.123155

SELECT convert(nvarchar, cast(@Test as money),1)

How do you secure your business logic layer

There are multiple ways of doing it.

WCF is one of solutions. Which exposes interfaces and not the implementation directly to the user.

OOPS - A nice object oriented design of an application is necessary.

What are diffgrams?

In a nut shell - using xml format to perform insert, update and delete operations on a table in database.

check the following URL
http://msdn.microsoft.com/en-us/library/aa257416(SQL.80).aspx