Re: Super PathKeys (Allowing sort order through precision lossfunctions) - Mailing list pgsql-hackers

From Nasby, Jim
Subject Re: Super PathKeys (Allowing sort order through precision lossfunctions)
Date
Msg-id 1B1681C7-5DAC-44E1-B4EA-E12509BA1A7F@amazon.com
Whole thread Raw
In response to Re: Super PathKeys (Allowing sort order through precision loss functions)  (Simon Riggs <simon@2ndquadrant.com>)
List pgsql-hackers
> On Oct 30, 2018, at 9:08 AM, Simon Riggs <simon@2ndquadrant.com> wrote:
> 
> On Tue, 30 Oct 2018 at 07:58, David Rowley <david.rowley@2ndquadrant.com> wrote:
>  
> I've started working on something I've ended up calling "Super
> PathKeys".  The idea here is to increase the likelihood of a Path with
> PathKeys being used for a purpose that requires a less strict sort
> order due to ordering being required from the return value of some
> precision loss function.
> 
> Anything left anchored would benefit, so SUBSTR(), TRIM() etc
> 
> Main use for this would be where the partition condition is a function, so we can still order by partitions easily.

This would also be very helpful in many BI cases; it’s very common to aggregate based on year, year/month,
year/quarter,etc.
 

The other thing that would be extremely useful would be pushing predicats through this, so you could do things like

WHERE date_trunc(‘year’, timestamp_field) = 2018

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