What is LISTEN and NOTIFY? LISTEN / NOTIFY is a feature that enables users to listen to what goes on in the database. It is one of the oldest functionalities in PostgreSQL and is still widely used. The main question is: What is the purpose of the asynchronous query interface (LISTEN / NOTIFY), and what […]

What are aliases in SQL? SQL aliases in FROM clauses are used to give a result set a temporary name. A result set may be produced by a table or view name, sub-SELECT and/or VALUES clause. An alias is created with the AS keyword, but the grammar allows us to omit it. An alias only […]

We all know and value SQL functions as a handy shortcut. PostgreSQL v14 has introduced a new, better way to write SQL functions. This article will show the advantages of the new syntax. An example of an SQL function Let’s create a simple example of an SQL function with the “classical” syntax so that we […]

Bonus cards, “Miles & more”, bonus points – don’t we all love and hate them at the same time? Recently we had an interesting use case which made me think about sharing some of the techniques we used in this area to reduce client code by writing some clever SQL. This post will show you […]

It’s been many years since the first ideas to implement the MERGE command surfaced on the PostgreSQL mailing list. Many years later, this important feature has finally made it into PostgreSQL core, and will (as of today) make it into PostgreSQL 15. To show people how this vital command works, I have decided to come […]

date_bin and timestamps in PostgreSQL Date and time are relevant to pretty much every PostgreSQL application. A new function was added to PostgreSQL 14 to solve a problem which has caused challenges for many users out there over the years: How can we map timestamps to time bins? The function is called date_bin. What people […]

Most of my readers will know about primary keys and all kinds of table constraints. However, only a few of you may have ever thought about the difference between a primary key and a UNIQUE constraint. Isn’t it all just the same? In both cases, PostgreSQL will create an index that avoids duplicate entries. So […]

In this article, I will answer the questions: why isn’t there a  SHOW TABLES command in PostgreSQL, when will SHOW TABLES in PostgreSQL be available, and how do I list tables with native PostgreSQL methods? Why isn’t there a SHOW TABLES command in PostgreSQL? People who come from MySQL are always asking the same question: […]

Most people in the SQL and in the PostgreSQL community have used the LIMIT clause provided by many database engines. However, what many do not know is that LIMIT / OFFSET are off standard and are thus not portable. The proper way to handle LIMIT is basically to use SELECT … FETCH FIRST ROWS. However, […]

© Laurenz Albe 2021 For many people, “cross join” is something to be afraid of. They remember the time when they forgot the join condition and the DBA was angry, because the query hogged the CPU and filled the disk. However, there are valid use cases for cross joins which I want to explore in […]

I decided to start out this year by looking into my notes from last year and extracting from them a small set of Postgres tips for you. This might not be, strictly speaking, fresh news… but I guess the average RAM of tech workers is about 64KB or so nowadays, so some repetition might not […]

In order to prepare for the start of training season (you can see our “stock” training offerings here by the way), I’ve updated our small “Postgres features showcase” project, and thought I’d echo it out too. Main changes – coverage on some features of the current v11 release and also from the upcoming v12. Short […]