MySQL Troubleshooting

Chapter 1. Basics

When troubleshooting, you can generally save time by starting with the simplest possible causes and working your way to more complicated ones. I work dozens of trouble tickets at MySQL Support every month. For most of them, we start from trivial requests for information, and the final resolution may—as we’ll see in some examples—be trivial as well, but sometimes we have quite an adventure in between. So it always pays to start with the basics.

The typical symptoms of a basic problem are running a query and getting unexpected results. The problem could manifest itself as results that are clearly wrong, getting no results back when you know there are matching rows, or odd behavior in the application. In short, this section depends on you having a good idea of what your application should be doing and what the query results should look like. Cases in which the source of wrong behavior is not so clear will be discussed later in this book.

We will always return to these basics, even with the trickiest errors or in situations when you would not know what caused the wrong behavior in your application. This process, which we’ll discuss in depth in Localizing the Problem (Minimizing the Test Case), can also be called creating a minimal test case.

Incorrect Syntax

This sounds absolutely trivial, but still can be tricky to find. I recommend you approach the possibility of incorrect SQL syntax very rigorously, like any other possible problem.

An error such as the following is easy ...