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

A couple of other thoughts depending on the size of the table with the large number of foreign keys (I may have missed the exact row counts), you might want to consider bitmaps on the foreign keys in the main table depending on the uniqueness of the data. Also, if the foreign key tables are relatively small another possibility to consider would be an indexed table if the joins would naturally grab the whole table.

Regards,

Bill Burke
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-----Original Message-----
Sent: Tuesday, January 07, 2003 2:59 AM
To: Multiple recipients of list ORACLE-L

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
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-----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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