I think experience should tell. When you have a slow query, look at the
plan. If it is using a FK index, look at the stadistics for that index.
If selectivity is >> 1 (how much? I think it depends on several factors,
hence the try-and-see procedure) then drop that FK and try the query again.

Ernesto Cullen


Alain PIERRE wrote:

>Thanks Milan for answering.
>
>6. pg 656 - The Lookup Table: "A lookup or control table is
>typically a static table with a small row count, which may
>be used in a similar way in several contexts. It consists of
>a small primary key and a description field, calculation
>factor, or some rule that processes need to refer to. ...
>Because one row in a lookup table supplies information to
>many rows, a slavish adherence to relational analysis rules
>often results in FK being bestowed on the lookup key columns
>of the user tables."
>
>Q6: Is there some rule of thumb/calculation rule to make
>up whether a table is to be considered as a lookup table or
>not. A threshold value of the index selectivity ?
>
>Anybody ?
>
>
>
>