Re: [HACKERS] CTE inlining - Mailing list pgsql-hackers

On 05/01/2017 04:33 PM, David G. Johnston wrote:> On Mon, May 1, 2017 at 7:26 AM, Andreas Karlsson <andreas@proxel.se>
  I am not sure I like decorators since this means adding an ad hoc>     query hint directly into the SQL syntax which
issomething which I>     requires serious consideration.>> ​Given that we already have> ​"​> prevent optimization> ​"​>
syntaxwhy do we need a decorator on the CTE?
 

I do not think I follow. Me and some other people here would ideally 
allow CTEs to be inlined by default. Some people today use CTEs as 
optimization fences, to for example control join order, and the 
suggestion here is to add new syntax for CTEs to allow them to 
selectively be used as optimization fences.
> ​I would shorten that to "WITH MAT" except that I don't think that> having two way to introduce an optimization fence
isworthwhile.
 

You mean OFFSET 0? I have never been a fan of using it as an 
optimization fence. I do not think OFFSET 0 conveys clearly enough to 
the reader that is is an optimization fence.

Andreas