Resolve 'mysqli_select_db() expects parameter 1 to be mysqli, string given' Error: Step-by-Step Guide

This guide will show you how to resolve the error 'mysqli_select_db() expects parameter 1 to be mysqli, string given' that you may encounter while working with PHP and MySQL. This error occurs when you pass incorrect parameters to the mysqli_select_db() function. By following the steps outlined in this guide, you can easily fix this issue and prevent it from happening in the future.

Table of Contents

• Understanding the Error
• Fixing the Error
• FAQ
• What is the purpose of the mysqli_select_db() function?
• Why am I getting this error?
• What is the difference between mysqli and mysql?
• Are there any alternatives to mysqli_select_db()?
• Can I still use the mysql extension instead of mysqli?

Understanding the Error

The mysqli_select_db() function is used to change the default database for the connection in PHP. It takes two parameters:

1. The MySQLi connection object
2. The name of the database you want to select

The error 'mysqli_select_db() expects parameter 1 to be mysqli, string given' occurs when you pass a string as the first parameter instead of the MySQLi connection object. This commonly happens when you mix up the order of the parameters.

For example, the following code will generate the error:

$connection = mysqli_connect("localhost", "username", "password");
$database = "my_database";
mysqli_select_db($database, $connection);

Fixing the Error

To fix the error, simply swap the order of the parameters in the mysqli_select_db() function. The correct order is:

1. The MySQLi connection object
2. The name of the database

Here's the corrected code:

$connection = mysqli_connect("localhost", "username", "password");
$database = "my_database";
mysqli_select_db($connection, $database);

By following this simple step, the error should be resolved, and your code should execute without issues.

FAQ

What is the purpose of the mysqli_select_db() function?

The mysqli_select_db() function is used to change the default database for the connection in PHP. This is useful when you are working with multiple databases and need to switch between them during the execution of your script. Learn more about mysqli_select_db()

Why am I getting this error?

You are getting this error because you passed a string as the first parameter to the mysqli_select_db() function instead of the MySQLi connection object. Ensure that you are passing the parameters in the correct order to resolve this issue.

What is the difference between mysqli and mysql?

mysqli stands for "MySQL Improved" and is an extension of the original mysql extension in PHP. The mysqli extension offers several improvements, including support for prepared statements, object-oriented programming, and enhanced debugging capabilities. In general, it is recommended to use the mysqli extension over the older mysql extension. Learn more about the differences between mysql and mysqli

Are there any alternatives to mysqli_select_db()?

Yes, you can use the mysqli::select_db() method, which is an object-oriented alternative to the mysqli_select_db() function. The usage is similar, but you call the method on the connection object instead of passing it as a parameter:

$connection = new mysqli("localhost", "username", "password");
$database = "my_database";
$connection->select_db($database);

Learn more about mysqli::select_db()

Can I still use the mysql extension instead of mysqli?

While the mysql extension was deprecated in PHP 5.5.0 and removed in PHP 7.0.0, it is strongly recommended that you use the mysqli extension or PDO (PHP Data Objects) instead. These alternatives offer more features, better security, and improved performance compared to the older mysql extension.