Re: How do FKs work?

On Sun, 10 Oct 2004, Janning Vygen wrote:

> Am Sonntag, 10. Oktober 2004 02:43 schrieb Marc G. Fournier:
>> On Sat, 9 Oct 2004, Tom Lane wrote:
>>> "Marc G. Fournier" <scrappy(at)hub(dot)org> writes:
>>>> Have a table with two FKs on it ... 2 different fields in the table
>>>> point to the same field in another table ...
>>>>
>>>> When I do an 'EXPLAIN ANALYZE DELETE FROM table WHERE field = #;', it
>>>> never comes back ... or, at lesat, takes a *very* long time ...
>>>
>>> Do you have indexes on the referencing columns? Are they exactly the
>>> same datatype as the referenced column? You can get really awful plans
>>> for the FK-checking queries if not.
>>
>> Yup, that was my first thought ... running SELECT's joining the two tables
>> on the FK fields shows indices being used, and fast times ...
>
> Why dont you try EXPLAIN DELETE ... (without ANALYZE). it shows you the plan
> without executing it and shows you which index is missing.

Thought about that too ... shows the index being used on the thable where
the delete is happening, but doesn't show anything as concerns the FKs
themselves ...

----
Marc G. Fournier Hub.Org Networking Services (http://www.hub.org)
Email: scrappy(at)hub(dot)org Yahoo!: yscrappy ICQ: 7615664