There are two different sort logics used by SQL Server to handle sorting! First one is the quick sort and another one is Merge sort. It begins sort in memory using Quick Sort algorithm but note that the memory requirement for this is at least 200% of its input rows size. Now if the memory grant is exceeded(even by a single byte), it spills entire immediate sort and remaining sort to disk. Then it will complete the sort on disk using Merge Sort algorithm.

Pawan Kumar Khowal

MSBISkills.com