Figure 1. Execution plan of a server query. As you can see in the above execution plan, SQL Server has highlighted a missing index that it thinks would help our query improve.

What is a query execution plan? SQL Server has an optimizer that usually does a great job of optimizing code for the most effective execution.

Because this operation is resource intensive, SQL Server will cache the execution plan in memory, and if the same query is executed again, it will reuse the execution plan.