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Posted by Gert-Jan Strik on 06/28/07 19:38
"news.onet.pl" wrote:
>
> > Select * From Quiz, Question Where Quiz.id = Question.id
>
> IMHO today inner join is a standard
>
> BTW left join is faster than inner join...
No it isn't.
For starters, an outer join (such as left join) will only return the
same result as an inner join if no rows from the outer table would be
eliminated when running the inner join.
Next, using inner join gives the optimizer more options how to process
the query which on average should lead to better performance then using
the outer join equivalent.
As usual, course there is a disclaimer here too. There could be
situations where the optimizer might select a suboptimal plan, or when
the optimizer shortcuts its optimization process because of the many
possible access paths. In those situations a rule based approach, or an
outer join approach might accidentally run faster.
Gert-Jan
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