Re: Optimization via explicit JOINs

On Fri, 9 Mar 2001, David Olbersen wrote:

> Greetings,
>   I've been toying aroudn with postgres 7.1beta5's ability to control the
>   planner via explicitely JOINing tables. I then (just for giggles) compare the
>   difference in the EXPLAIN results.
> 
>   I'm no super-mondo-DBA or anything, but in my two attempts so far, the numbers
>   I get out of EXPLAIN have been about 1/2 as small.
> 
>   Below are two EXPLAIN results, am I correct in reading that one is indeed
>   "twice as fast" as the other? I say twice as fast because the top-most cost in
>   the first query is 58.62, but in the second one it's only 32.09. Am I reading
>   this correctly?

Not entirely.  Those are only estimates, so they don't entirely line up
with reality.  Also, I notice the first estimates 14 rows and the second
1,  which is probably why the estimate is higher.  In practice it probably
won't be significantly different.