PostgreSQL trigger consistency check

Introduction In this article, we are going to see how to implement a non-trivial consistency check using a PostgreSQL INSERT and UPDATE trigger. By using a database trigger after executing an INSERT or UPDATE, we can ensure that the sum of salaries in a given department does not exceed the maximum budget allocated for the given department.

A beginner’s guide to database deadlock

Introduction In this article, we are going to see how a deadlock can occur in a relational database system, and how Oracle, SQL Server, PostgreSQL, or MySQL recover from a deadlock situation.

JDBC Driver Maven dependency list

Introduction Ever wanted to connect to a relational database using Java and didn’t know which JDBC Driver Maven dependency to use? If so, this article is surely going to help you from now on.

Mapping PostgreSQL Interval to Java Duration with Hibernate

Introduction In this article, we are going to see how to map the PostgreSQL interval column type to a Java Duration object using Hibernate and the hibernate-types project. Another very useful feature introduced by the hibernate-types project is that all types extending the ImmutableType can now be treated as standard org.hibernate.type.Type, therefore enabling a much better Hibernate Core API integration.

How to limit the SQL query result set to Top-N rows only

Introduction In this article, we are going to see how we can limit the SQL query result set to the Top-N rows only. Limiting the SQL result set is very important when the underlying query could end up fetching a very large number of records, which can have a significant impact on application performance.

SQL ORDER BY RANDOM

Introduction In this article, we are going to see how we can sort an SQL query result set using an ORDER BY clause that takes a RANDOM function provided by a database-specific function. This is a very handy trick, especially when you want to shuffle a given result set. Note that sorting a large result set using a RANDOM function might turn out to be very slow, so make sure you do that on small result sets. If you have to shuffle a large result set and limit it afterward, then it’s… Read More

How to implement a database job queue using SKIP LOCKED

Introduction In this article, we are going to see how we can implement a database job queue using SKIP LOCKED. I decided to write this article while answering this Stack Overflow question asked by Rafael Winterhalter. Since SKIP LOCKED is a lesser-known SQL feature, it’s a good opportunity to show you how to use it and why you should employ it, especially when implementing a job queue task.

How does a relational database execute SQL statements and prepared statements

Introduction In this article, we are going to see how a relational database executes SQL statements and prepared statements.

How to map a PostgreSQL Range column type with JPA and Hibernate

Introduction In this article, we are going to see how to map the PostgreSQL range column types with JPA and Hibernate. Luckily, you don’t have to implement a custom Hibernate type for the PostgreSQL range column type since the hibernate-types project already provides support for it.

How to map a PostgreSQL HStore entity property with JPA and Hibernate

Introduction The open-source hibernate-types project allows you to map a great variety of database types that are not supported natively by Hibernate ORM (e.g. JSON, ARRAY, YearMonth, Month, INET addresses). In this article, we are going to see how you can map a PostgreSQL HStore type, which allows you to store key/value pairs, to a Java Map entity property when using JPA and Hibernate.