More than that, a really good hash function would produce unique
reproducible output for each distinct input. Such hash functions are
referred to as cryptographically strong and are used for message
authentication. The idea is that being applied over a message, the
function produces unique hash value which can be verified by
receiver by applying the same function and comparing the hash
value. Simpler hash functions are usually used for fast node
grouping and search. As far as I understood, the hash join
works by creating a table of hash values for one table and then
filtering columns from the second table by throwing away
columns whose hash is not in hash table and quickly finding the
join target row otherwise.
--
Vladimir Zakharychev (bob@dpsp-yes.com) http://www.dpsp-yes.com
Dynamic PSP(tm) - the first true RAD toolkit for Oracle-based internet applications.
All opinions are mine and do not necessarily go in line with those of my employer.
"Jonathan Lewis" <jonathan_at_jlcomp.demon.co.uk> wrote in message
news:1016721483.26795.0.nnrp-10.9e984b29_at_news.demon.co.uk...
>
> A hash function or method is a function
> that has a limited list of possible output
> values. When supplied with a large list of
> input values, a good hash function will distribute
> the input randomly, evenly, and reproducibly
> across its list of outputs.
>
> --
> Jonathan Lewis
> http://www.jlcomp.demon.co.uk
>
> Next Seminar - UK, April 3rd - 5th
> http://www.jlcomp.demon.co.uk/seminar.html
>
> Host to The Co-Operative Oracle Users' FAQ
> http://www.jlcomp.demon.co.uk/faq/ind_faq.html
>
> Author of:
> Practical Oracle 8i: Building Efficient Databases
>
>
>
>
Received on Fri Mar 22 2002 - 08:38:04 CST
