Subject | Re: [ib-support] Db Design opinions sought - Lookup tables and surrogate PKs |
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Author | Helen Borrie |
Post date | 2002-07-26T23:30:37Z |
At 11:52 AM 26-07-02 -0700, you wrote:
relationship and let cascades do their thing. There is a significant
problem with this, however. If you apply RI to a lookup key, an
single-column index will be created for the lookup key. Single-column
indexes on lookup columns typically have very low selectivity, which kills
performance - every time, not just when a key value changes. So RI on
lookup columns is best avoided...
heLen
All for Open and Open for All
Firebird Open SQL Database · http://firebirdsql.org ·
http://users.tpg.com.au/helebor/
______________________________________________________________________
>Yes in general i feel the int is the way to go but re: changed spelling andTechnically, yes, it is possible to apply ref integrity to such a
>all of the changes to other tables, a foriegn key relationship with the
>cascading referential integrity will do the updates for you..albeit in some
>cases it could be a slow update! Space in that scenario is definitely an
>issue but not in smaller apps.
relationship and let cascades do their thing. There is a significant
problem with this, however. If you apply RI to a lookup key, an
single-column index will be created for the lookup key. Single-column
indexes on lookup columns typically have very low selectivity, which kills
performance - every time, not just when a key value changes. So RI on
lookup columns is best avoided...
heLen
All for Open and Open for All
Firebird Open SQL Database · http://firebirdsql.org ·
http://users.tpg.com.au/helebor/
______________________________________________________________________