Re: Foreign key & User defined Index Difference

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#471

From: Quinn Wildman (CodeGear Develope...
Date: Mon, 03 Dec 2007 17:39

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The optimizer used to have priority level something like this:

1. keys
2. unique indexes
3. foreign keys
4. indexes with highest selectivity

I belive it is now:

1. keys
2. unique indexes
3. indexes with highest selectivity

Does this explain it?

Bill Todd wrote:
> Quinn Wildman (CodeGear Developer Support) wrote:
> 
>> Depending on your version of InterBase, foreign keys may have a
>> higher selectivity. So, the optimizer may choose to do things
>> differently for foreign keys vs user defined indexes.
> 
> Could you expand on that? How can two identical indexes have different
> selectivity just because one was created automatically as part of a
> foreign key and one was created with CREATE INDEX?
>

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