Every so often someone needs solution to getting first (or couple of first) values for given column. Or last.
For some cases (when there is not many groups) you can use recursive queries. But it's not always the best choice.
Let's try to implement first() and last() aggregates, so these could be easily used by anybody.
Couple of people asked, on irc, about how to generate unique, short, ids for rows.
Since I wrote code for this for explain.depesz.com, I figured that instead of pointing to sources, and letting everyone to extract the functions, I will, instead, write a set of functions that what is needed in reusable way.
On 3rd of October, Andres Freund committed patch:
Add CASCADE support for CREATE EXTENSION. Without CASCADE, if an extension has an unfullfilled dependency on another extension, CREATE EXTENSION ERRORs out with "required extension ... is not installed". That is annoying, especially when that dependency is an implementation detail of the extension, rather than something the extension's user can make sense of. In addition to CASCADE this also includes a small set of regression tests around CREATE EXTENSION. Author: Petr Jelinek, editorialized by Michael Paquier, Andres Freund Reviewed-By: Michael Paquier, Andres Freund, Jeff Janes Discussion: <a class="text" href="/gitweb/?p=postgresql.git;a=object;h=557E0520">557E0520</a>.3040800@2ndquadrant.com
Continue reading Waiting for 9.6 – Add CASCADE support for CREATE EXTENSION.
There exists an extension to PostgreSQL, which lets you use hypothetical indexes.
What are there? That's simple – these are indexes that don't really exist. So what good are they?
Let's see.