Re: Are too many Foreign Keys in one table bad?

And apart from the differences in cost on the simple test, you also remove the information about uniqueness and non-nullability if you don't declare the primary key, and this has an impact on the optimizer's decision tree.

Bear in mind, also, that Oracle will rarely do a tablescan on the inner table of a nested loop - so you may get a fifteen table hash join if you don't have any indexes, and this MIGHT go to one of the two possible extremes of demanding nearly 14 x hash_area_size in memory, or 14 allocations of temporary extents on your temporary tablespace.

Regards

Jonathan Lewis
http://www.jlcomp.demon.co.uk

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The Co-operative Oracle Users' FAQ
http://www.jlcomp.demon.co.uk/faq/ind_faq.html

-----Original Message-----
To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com> Date: 07 January 2003 02:45

>
>There can be quite a difference between using
>an index on a small table, and not using one.
>

-- 
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Author: Jonathan Lewis
  INET: jonathan_at_jlcomp.demon.co.uk

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