[dba-SQLServer] SQL Server Hash algorithm - question,

On 5 Sep 2004 at 10:44, John W. Colby wrote:

> MATCH FIELD!  That's the name they called it.  What I haven't discovered is
> whether the field is actually required or whether a unique index on all
> these fields prevents dupes and I'm done.  It seems like an extra step to
> pull those X characters out, append them all together, then drop them in a
> new field.  They insist that it is needed but they don't understand
> databases.  I understand databases but I don't know their business.
> 
> I suspect that this new "match field" is then indexed to prevent dupes.  Is
> it used for anything else?  Is it a standard definition (how many characters
> from which fields)?
> 

I doubt that there is a standard.  "Match field" seems to be to just be 
another name for "natural key"  (At least a qick scan of the some googles 
on this suggest so)

If you create a field which contains a hash derived from x characters from 
a number of fields (where x varies according to the field , but is less 
than the maximum record length) and index that,  it will make the index 
file smaller than indexing the fields directly  and should be faster than a 
multi field index.

"Match Field  v Natural Key" looks to me like one of those arguments where 
the best solution depends on the type of data in use and the specifics of 
the db engine being used.





-- 
Stuart