> if you study engine internals, especially MergeJoin, HashJoin, NestedLoopJoin it's called merge join because it employs the merge algorithm (linear time cons

> if you study engine internals, especially MergeJoin, HashJoin, NestedLoopJoin it's called merge join because it employs the merge algorithm (linear time constant space)[1] - this can only be used when the inputs are sorted. likewise the hash join entails building a hash table and using it (linear time linear space)[2] but the inputs don't have to be sorted. the point of these is to avoid the O(N*M) nested loop [1] https://en.wikipedia.org/wiki/Merge_algorithm https://en.wikipedia.org/wiki/Merge_algorithm [2] https://en.wikipedia.org/wiki/Hash_join https://en.wikipedia.org/wiki/Hash_join