1. Block comments are typically used at the beginning of a T-SQL code to provide an explanation about the purpose of the code.
2. The following example contains a block comment that describes the purpose of the T-SQL code. Comments are enclosed within the /* and */ elements.

/* The purpose of the Transact-SQL 
statement below is to retrieve the 
Firstname and Lastname of StudentID 1 */

USE Adventureworks
GO
SELECT Firstname, Lastname
FROM students
WHERE StudentID = 1

1. In-line comments are added within the T-SQL code to add descriptive comments to portions of the code.
2. In-line comments begin with -- (two hyphens). Any characters to the right of this are commented out on the line where the -- are placed, and are excluded from the T-SQL statement. Comments inserted with -- are terminated by the newline character.
3. Additional elements can also be used to add flexibility and logic to any T-SQL statements. These elements can add dynamic capabilities to your statements and logic, and provide you with the ability to create powerful T-SQL statements
4. The following is an example of an in-line comment within a T-SQL statement.

USE Adventureworks
GO
SELECT Firstname, Lastname 
FROM students
WHERE StudentID = 1 -- Only StudentID one is returned