What is a query execution plan?

A query execution plan is an internal representation of how a DBMS or ORM will execute a specific database query. It describes a sequence of operations such as table scans, index usage, table joins, sorting, and filtering.

In the context of C# and, for example, Entity Framework, when you write a LINQ query, it is translated into SQL, and then the database builds an execution plan to retrieve the data efficiently.

Understanding the execution plan helps optimize queries, identify bottlenecks, and improve application performance.

Example: if a query retrieves data with filtering on a non-indexed field, the execution plan may include a full table scan, which is slower than using an index.