When you need to extract data from the database you are writing, more or less complex, T-SQL code. Often simplistic and procedural approach reflects what you have in your mind, however this could have a negatively impact about performance because the database engine might think otherwise. Fortunately T-SQL, as a declarative language, allows us to ask the "what" and delegate to the engine the "how". Everything works best as long as you respect a few simple rules and you may use special constructs. In this session, with few slides and a lot of real-case scenarios, you can see the advantages of writing the query for high performance, even when they are written by that "someone else" called ORM.