Common Table Expressions (CTEs) are a very useful tool and frankly a big improvement on sub-queries.  But there are differences in how they are implemented in MySQL and MariaDB.  That  is not too surprising since the code fork many years ago. Different engineers implementing the same idea will have different approaches (and sometimes results). But differences in implementation are often important and, in this case, shockingly different.

Jesper Wisborg Krogh at Oracle OpenWorld and CodeOne gave a series of presentations and hands on labs that were excellent. He is an amazing Support Engineer and a great presenter of material at conferences.  In the lab for Common Table Expressions he did point out to me an interesting problem in MariaDB's implementation of CTEs. 

The Problem In a Nutshell
On the PostgreSQL Wiki, there is a
an SQL query (requires PostgreSQL 8.4 or MySQL 8.0) that …

I am happy that the MySQL team is, during the last years, blogging about each major feature that MySQL Server is getting; for example, the series on Recursive Common Table Expressions. Being extremely busy myself, …

This post wants to be:1. A quick glance at the new "common table expression" (aka hierarchical queries) in Firebird 2.12. A call to action for other opensource databasesSo, on with 1., Firebird recently added another great feature, common table expressions (CTE) which, to my eye at least, boils down to hierarchical queries.This is basically the ability to efficiently and easily query hierarchical