11 Articles tagged “Sql”

In our article Exploring a Data Set in SQL we discovered a data set related to music: the Chinook sample database.

Our discovery led us to find albums containing tracks of multiple genres, and for the analytics we were then pursuing, we wanted to clean the data set and assign a single genre per album. We did that in SQL of course, and didn’t actually edit the data.

Finding the most frequent input value in a group is a job for the mode() WITHIN GROUP (ORDER BY sort_expression) Ordered-Set Aggregate Function, as documented in the PostgreSQL page about Aggregate Functions.


Today is the day my book Mastering PostgreSQL in Application Development launches! I’m all excited that everybody interested is now able to actually read my book! Mastering PostgreSQL in Application Development targets application developers who want to learn SQL properly, and actually master this programming language. Most developers don’t think of SQL as a programming language, mainly because they don’t have full control of the execution plan of their queries.

Mastering PostgreSQL in Application Development is the full title of the book I am currently writing. Running the PostgreSQL is YeSQL series of blog posts has shown me developers need a PostgreSQL book for developers. A book with the same properties as the YeSQL series articles in this blog: we use real world data sets to put every query and SQL technique we learn in the context of a user story or business case,

In a previous article here we saw How to Write SQL in your application code. The main idea in that article is to maintain your queries in separate SQL files, where it’s easier to maintain them. In particular if you want to be able to test them again in production, and when you have to work and rewrite queries.


The reason why I like Unicode a lot is because it allows me to code in text based environments and still have nice output. Today, we’re going to play with Regional Indicator Symbol, which is implemented as a Unicode combinaison of letters from 🇦 to 🇿. For instance, if you display 🇫 then 🇷 concatenated together, you get 🇫🇷. Let’s try that from our PostgreSQL prompt!

The modern calendar is a trap for the young engineer’s mind. We deal with the calendar on a daily basis and until exposed to its insanity it’s rather common to think that calendar based computations are easy. That’s until you’ve tried to do it once. A very good read about how the current calendar came to be the way it is now is Erik’s Naggum The Long, Painful History of Time.


Business logic is supposed to be the part of the application where you deal with customer or user facing decisions and computations. It is often argued that this part should be well separated from the rest of the technical infrastructure of your code. Of course, SQL and relational database design is meant to support your business cases (or user stories), so then we can ask ourselves if SQL should be part of your business logic implementation. Or actually, how much of your business logic should be SQL?


Sometimes you need to dive in an existing data set that you know very little about. Let’s say we’ve been lucky to have had a high level description of the business case covered by a database, and then access to it. Our next step is figuring out data organisation, content and quality. Our tool box: the world’s most advanced open source database, PostgreSQL, and its Structured Query Language, SQL.


Dimitri Fontaine

PostgreSQL Major Contributor

Open Source Software Engineer

France