What is a query plan?

Think of a query execution plan as a map that provides information on the physical operators that implement the logical operations discussed in the Understanding Query Processing chapter, as well as the execution context for that query that provides information about the system on which the query was executed. Each physical operator is identified in the plan with a unique node ID.

Note

Query execution plans are often referred to as a showplan, which is a textual, XML, or graphical representation of the plan.

So far, we’ve used the terms query plan and query execution plan interchangeably. However, in the SQL Database Engine, there is the notion of an “actual plan” and an “estimated plan.” These differ only in the fact that an “actual plan” has runtime data collected during actual execution (hence, query execution plan), whereas an “estimated plan” is the output of the Query Optimizer that...