Question: What is
the 12.2 new feature called a "band join". How does
this band join differ from other join types?
Answer: The Oracle 12 release 2
software release a new join type called a band join.
The Oracle docs note that the band join is a special type of
non-equijoin in which key values in one data set must fall
within the specified range (“band”) of the second data set.
The same table can serve as both the first and second
data sets. Starting in Oracle Database 12c Release 2 (12.2),
the database evaluates band joins more efficiently. The
optimization avoids the unnecessary scanning of rows that
fall outside the defined bands. The optimizer uses a cost
estimate to choose the join method (hash, nested loops, or
sort merge) and the parallel data distribution method. In
most cases, optimized performance is comparable to an
equijoin.
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