Some Doubts about LINQ in c#

Technically correct but it misses the point. You can put SQL statements in your program as well. Linq is an object query language that allows a standard way of querying different types of data sources (XML, SQL, POCOs, etc.) When talking about accessing SQL, you can do the same thing with Linq as you can with a TSQL statement (both in your code). Because of the efficiency of Linq, it is practically the same in terms of performance as making the SQL call from code. My suggestion would be to learn more about Linq and figure out what you are trying to do exactly to see if Linq is the right choice.