Re: improving a badly optimized query

Brandon Craig Rhodes <brandon(at)oit(dot)gatech(dot)edu> writes:
> Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
>> It seems like a useful optimization, but I have an uncomfortable
>> feeling that there's something wrong with it. Can you point to a
>> rigorous proof that this is okay in complicated contexts such as
>> nested outer joins?

> We can optimize the above query simply by observing that the result of
> a LEFT JOIN includes both the rows that would have been produced by a
> simple JOIN, and those rows of the left table that did not match any
> from the right. [snip]

You didn't answer my question: when there are *nested* outer joins, how
does this transformation apply? Can a clause from WHERE or an
upper-level JOIN/ON clause be pushed down past one outer join and into
another?

regards, tom lane