The Query Processor is also the component inside the SQL Server Database Engine that is responsible for query optimization. This is the second stage of query processing and its goal is to produce a query plan that can then be cached for all subsequent uses of the same query. In this section, we will focus on the highlighted sections of the following diagram, which handle query optimization:
SQL Server uses cost-based optimization, which means that the Query Optimizer is driven mostly by estimations of the required cost to access and transform data (such as joins and aggregations) that will produce the intended ...
