Introducing query processing and execution
To better understand the factors that affect query performance, to understand how to spot potential performance problems with a query plan, and ultimately to learn how to use query optimizer hints to tune individual query plans, we first need to understand how the SQL Server query processor executes queries. This section introduces iterators, one of the most fundamental query execution concepts; discusses how to read and understand query plans; explores some of the most common query execution operators; and shows how SQL Server combines these operators to execute even the most complex queries.
SQL Server breaks queries down into a set of fundamental building blocks called operators or iterators. ...