A Hash Match is a blocking operator that represents a Hash join operation in an execution plan. Hash joins are the most efficient way to join two large input that are not sorted and/or do not have any indexes that support the join. A Hash Match operation is expensive in that it consumes a significant amount of memory and CPU and may generate additional I/O if it does not fit in memory, but it is generally faster than both Nested Loops and Merge Joins when joining a large number of unsorted rows.
With a Hash Match, the Outer Table is also referred to as the Build Table and the Inner Table is referred to as the Probe Table. The smaller of the two input will be chosen as the Build Table, which will be used to build a hash table ...
