PostgreSQL 9.4 extends the SQL standard by inserting two new clauses that facilitate many operations required during the development of applications: the WITHIN GROUP and FILTER clauses.
As part of AXLE project work I recently found myself re-examining issues around optimisation fencing and non-semantic query execution changes in PostgreSQL. One key issue was the inability to use a CTE where optimisation (inlining, push-up/pull-down, flattening, etc) was desired. I’d like to explain that in more detail, as it’s something that can surprise new […]
An interesting query has been twitted by Will Leinweber from Postgres Open: — this returns a different result each time it is ran with recursive s as ( select random() union select random() from s ) select count(*) from s; I like this example: a surprising result, which can be explained by (and indeed helps to explain) CTE […]