Re: Performance Issues (was: "like" vs "substring" again)

Christian Schröder wrote:

> Or would it be possible to tweak how the planner determines the  
> selectivity? I have read in the docs (chapter 54.1) that in case of  
> more than one condition in the where clause, independency is  
> assumed. In my case ("... where test like '11%' and test not like  
> '113%'") this is clearly not the case, so it might be an  
> interesting point to address.

I think the planner does think about the interactions of  
inequalities, so if you can express your query with less-than and  
friends, or even with BETWEEN, you might get a better plan.  I don't  
know the details of your setup, but you can do things like this with  
any ordered type:

    where test between '11' and '113'
	or test >= '114'

I know this does not match the exact semantics of your query, but  
hopefully you get the idea.

- John D. Burger
   MITRE