Distinct hash table scan icon

Distinct Hash Table Scan

The Distinct Hash Table Scan icon indicates that the entire temporary distinct hash table will be scanned and all of the entries contained with the hash table will be processed. A distinct hash table scan is generally considered when optimizer is considering a plan that requires the data values to be collated together and all duplicate removed but the sequence of the data is not required. The use of a distinct hash table scan will allow the optimizer to generate a plan that can take advantage of any non-join selection while creating the temporary distinct hash table. An additional benefit of using a distinct hash table scan is that the data structure of the temporary distinct hash table will usually cause the table data within the distinct hash table to remain resident within main memory after creation thus reducing paging on the subsequent scan operations.

Also referred to as: Distinct Hash Table Scan, Preload; Distinct Hash Table Scan Distinct; Distinct Hash Table Scan Distinct, Preload