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Home -> Community -> Usenet -> c.d.o.misc -> Re: HASH-JOIN
> If I remember correctly: the first pass builds a hash table
> for relation A on values of the join attribute, say, A.1. The
> second pass then scans the second relation B and applies the same
> hashing function to join attribute B.1. When B.1 hits A.1 and
> a corresponding check reveals that A.1 equals B.1, the joined
> rows are generated. It's faster than a merge since nothing need
> be sorted.
Yup, thats right. Hash join works best where you are joining a little table to a big table - ideally the hash should be built against the little table, and should fit into memory for best performance. I think has join is really targetted at Decision Support applications
-- Alan Burlison alanburlison_at_unn.unisys.com My opinions may be incorrect, but they are my own.Received on Sun Jan 26 1997 - 00:00:00 CST