© Laurenz Albe 2022 I have been faced with a request for an unusual unique constraint that puzzled me for a while. Since the solution I came up with is a nice show-case for range data types, I’ll share it with you. Also, it allows me to rant some about NULL, which is a temptation […]

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 PostgreSQL and many other relational databases, constraints are an integral part of the feature set. Many people are aware of primary keys, foreign keys, CHECK-constraints, table constraints and so on. However, from time to time, the situation is way more complicated. That’s when some more advanced techniques are needed to enforce integrity in the […]

In SQL, the concept of foreign keys is an important one that can be found in all professional databases used in the industry. The core idea is to prevent your PostgreSQL database from storing inconsistent data by enforcing constraints ensuring the correctness of your tables (at least as far as relations between objects are concerned). […]

  Sometimes you want to enforce a condition on a table that cannot be implemented by a constraint. In such a case it is tempting to use triggers instead. This article describes how to do this and what to watch out for. It will also familiarize you with the little-known PostgreSQL feature of “constraint triggers”. […]