Re: order of nested loop

Tom Lane wrote:
> 
> Jean-Luc Lachance <jllachan@nsd.ca> writes:
> > I am currious.  Why perform a sort first?  Would it not be more
> > efficient to create an in memory index on the fly?
> 
> Why would you think that?  Creating an index involves a sort ...
> there's no free lunch there that I can see.
> 
>                         regards, tom lane


There is only a small difference, but distinct implies unique index
which mean there is no need to sort duplicate records.