Re: Problem with slow query with WHERE conditions with OR clause on primary keys

kolszew73@gmail.com wrote
> Thanx for your answer
>
> My example is trivial because i want to show strange (for me) postgres
> behavior with dealing with primary keys (extreme example), in real
> situation user put search condition e.g.  "Panas" and this generates query
> ...
> where gd.other_code like 'Panas%' OR g.code like 'Panas%'
> ..
>
> both columns has very good indexes and selectivity for "like 'Panas%'" ...
>
> I have experience from Oracle with this type of queries, and Oracle have
> no problem with it,
> executes select on index on other_code from gd and join g
> in next step executes select on index on code from g and join gd
> and this two results are connected in last step (like union)
> very fast on minimal cost
>
> and in my opinion read whole huge tables only for 10 rows in result where
> conditions are very good  ... is strange

I suppose the equivalent query that you'd want would be:

SELECT ... FROM gd JOIN gd_data USING (id_gd)
WHERE id_gd IN (

SELECT id_gd FROM gd WHERE ...
UNION ALL -distinct not required in this situation
SELECT id_gd FROM gd_data WHERE ...

) --ignoring NULL implications

It does make sense conceptually...

David J.






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