Learn T-SQL Querying

The Exploration stage

If the Trivial Plan stage doesn't find a suitable plan, it's time to enter the cost-based optimization stage, known as Exploration, whose goal is to find a good-enough query execution plan based on the minimum estimated cost to access and join data. If this stage is used, the information on the optimization level is still stored in the execution plan under the same Optimization Level property, with a value of FULL.

A good-enough plan refers to the search optimization space and how SQL Server may not actually iterate through all possible plan combinations, but rather may look for a plan that meets its internal thresholds for a good-enough balance between the estimated resource usage and execution times.

The Exploration ...